function

function — noun

1. the main job, use, or reason that something or someone exists within a system or

1.nounB1
Definition

the main job, use, or reason that something or someone exists within a system or situation

Example

The main function of a refrigerator is to keep food cold and fresh.

function of — purpose/use pattern

Christopher's function in the team is to manage the project budget and timeline.

Common collocations
  • serve a function
  • perform a function
  • main function
  • primary function
  • specific function
Synonyms
  • purpose

    more common for the intended reason something exists; function focuses on the job it does in a system

  • role

    emphasizes expected contribution within a group, especially of a person

  • use

    more practical and concrete; tells you how to employ something

  • duty

    restricted to moral or professional obligations of a person

Grammar Patterns

function of [noun]

serve/perform/have a function

Common Mistakes

The function of the meeting is for discussing the budget.
The purpose of the meeting is to discuss the budget.
For the reason behind an event or plan, 'purpose' or 'point' is more natural than 'function'.

2. a large, formal gathering of people for a ceremony, celebration, or official occ

2.nounB2
Definition

a large, formal gathering of people for a ceremony, celebration, or official occasion

Example

The ambassador attended a formal function at the city museum last night.

formal function — formal social event

Élise wore a long gown to the charity function at the grand hotel.

Common collocations
  • charity function
  • formal function
  • diplomatic function
  • host a function
  • fundraising function
Synonyms
  • event

    more general; can be formal or informal, large or small

  • gathering

    softer, less formal tone; any group of people meeting

  • ceremony

    specifically religious or ritualistic; more solemn than a function

Grammar Patterns

[adjective] function

function at [venue]

Usage Note

Often paired with adjectives that describe the type of event, such as 'charity function', 'diplomatic function', or 'fundraising function'. Not used for small, informal gatherings with friends.

Common Mistakes

I invited a few friends over for a small function at my flat.
I invited a few friends over for a small party at my flat.
'Function' is for formal, organised gatherings, not casual get-togethers.

3. the way a machine, system, or living body behaves and carries out its tasks

3.nounB2
Definition

the way a machine, system, or living body behaves and carries out its tasks

Example

The brain's function depends on a steady supply of oxygen and nutrients.

body/organ + function — physiological operation

Hiro noticed that the function of the old engine had become less smooth.

Common collocations
  • bodily function
  • organ function
  • proper function
  • normal function
  • impaired function
  • brain function
Synonyms
  • operation

    more technical; used especially for machines and formal systems

  • performance

    focuses on how well something works, not simply that it works

  • working

    more informal; common in everyday speech about devices

Grammar Patterns

[noun] function

function of [organ/system/machine]

Usage Note

Frequently used with body parts or physiological systems (liver function, brain function, immune function) and machines (engine function, system function). Often modified by adjectives describing quality, such as 'normal function', 'proper function', or 'impaired function'.

Common Mistakes

I checked the function of my phone by looking at its colour.
I checked whether my phone was functioning by making a call.
This sense describes how something operates, not its external features or condition.

4. a named block of code in a computer program that performs a specific task when a

4.nounB2
Definition

a named block of code in a computer program that performs a specific task when activated

Example

The search function lets you find any file on your computer by name.

search/sort + function — software feature

Kofi wrote a function in Python that calculates the average temperature.

Common collocations
  • call a function
  • define a function
  • write a function
  • search function
  • login function
  • function call
Synonyms
  • routine

    older term; less common in modern programming than 'function'

  • method

    used in object-oriented programming; a function that belongs to a class

  • procedure

    similar to function but does not return a value

Grammar Patterns

call/define/use a function

[noun] function

Usage Note

In programming, a function is a reusable block of code. Common verb collocations include 'call a function', 'define a function', and 'write a function'. In everyday software use (apps, websites), 'function' can also refer to a feature or tool (e.g. 'search function', 'sort function').

Common Mistakes

I need to replace a function in my computer's hardware.
I need to fix the login function in my program's code.
In computing, 'function' refers to software code, not physical hardware parts.

5. a relationship where one thing directly depends on or varies with another

5.nounC1
Definition

a relationship where one thing directly depends on or varies with another

Example

In economics, supply is a function of demand and production costs.

X is a function of Y — dependency pattern

The quality of a crop is a function of rainfall and soil conditions.

Common collocations
  • function of
  • is a function of
  • direct function of
Synonyms
  • dependence

    noun form that directly states the relying relationship

  • correlation

    weaker than function; implies two things change together without one causing the other

Grammar Patterns

X is a function of Y

Usage Note

Typically appears in the pattern 'X is a function of Y', meaning X depends on Y or is determined by Y. Common in academic, economic, and technical writing. This sense does NOT refer to a specific job or purpose (noun 1).

Common Mistakes

His happiness is a function of his new car.
His happiness depends on many factors, not just his new car.
'Is a function of' suggests a direct, measurable dependency. For personal emotions, 'depends on' is more natural.

6. a rule in mathematics that connects each input value to exactly one output value

6.nounB2
Definition

a rule in mathematics that connects each input value to exactly one output value

Example

In the equation y = 2x + 1, y is a function of x.

function of x — mathematical relationship

The maths teacher asked the class to graph the function f of x equals x squared.

Common collocations
  • linear function
  • quadratic function
  • graph a function
  • inverse function
  • function of x
  • function f(x)
Synonyms
  • mapping

    more informal term that describes how inputs are paired with outputs

  • relation

    broader category; every function is a relation, but not every relation is a function

Grammar Patterns

function of [variable]

function f(x)

[adjective] function

Usage Note

Distinguish from the computing sense (noun 4): in mathematics, a function is an abstract relationship between numbers, not a block of computer code. Common phrases include 'function of x', 'linear function', 'quadratic function', 'inverse function', and 'graph a function'.

Common Mistakes

A function always goes up on the graph.
A function can go up, down, or stay flat
it only needs to give one output for each input.' — The defining feature of a mathematical function is the one-output-per-input rule, not the shape of its graph.

function — verb

Word family

Synonym discussion

Sense: noun/1

Function, purpose, role, use, and duty all describe what something or someone is meant to do, but each word emphasises a different angle. Function focuses on the specific job or activity something performs as part of a larger system — 'The function of the brake pedal is to stop the car.' Purpose highlights the intended reason something exists — 'The purpose of the meeting is to reach a decision.' Use is more practical and concrete; it tells you how something can be employed — 'This tool has many uses in the kitchen.' Role emphasises a person's or thing's expected contribution within a group or situation — 'Her role in the team is to check the data for errors.' Duty is restricted to moral, professional, or legal obligations, and only applies to people — 'It is the duty of a lifeguard to watch the swimmers.' For example: 'The main function of a thermostat is to control temperature (its job in the system), but its purpose is to keep the room comfortable (the reason).' While function can apply to both people and things, duty only works for people, and use rarely applies to people in this sense.

purpose ↗role ↗use ↗duty ↗

Common collocations

Nouns

Adverbs

Prepositions

Etymology

LatinFrenchEnglish

Function comes from the Latin word 'functio', meaning 'performance or execution', which in turn comes from the verb 'fungi' meaning 'to perform, carry out, or discharge a duty'. It travelled into English through Middle French as 'fonction' in the late 1400s. The mathematical meaning — a relationship between values — developed in the 1700s as scholars needed a term for a quantity that 'performs' a mapping from one set of numbers to another. The computing sense followed in the mid-1900s as programmers adopted the mathematical idea of a function as a self-contained block of code that takes input and returns output.