deficient

deficient — adjective

1. containing less of something than what is necessary to stay healthy, function we

1.adjectiveB2
Definition

containing less of something than what is necessary to stay healthy, function well, or achieve a goal.

Example

Niran's diet was deficient in iron, so the doctor gave him supplements.

deficient in [nutrient]

The soil in this region is deficient in nitrogen, which affects crop growth.

Common collocations
  • deficient in vitamins
  • deficient in iron
  • deficient in nutrients
  • deficient in evidence
  • deficient in resources
Synonyms
  • lacking

    less formal, used in everyday speech

  • insufficient

    focuses on quantity or amount being too low

  • inadequate

    emphasises that the amount fails to meet a specific need

Antonyms

Grammar Patterns

deficient in + [noun]

Usage Note

Frequently used with the preposition 'in' to specify what is lacking. Common in medical, nutritional, and academic writing. Not used in informal conversation about everyday shortages — for those, use 'short of' or 'low on'.

Common Mistakes

The soup was deficient of salt.
The soup was deficient in salt.
The correct preposition after 'deficient' is 'in', not 'of'.

2. below an acceptable standard of quality, completeness, or performance.

2.adjectiveB2
Definition

below an acceptable standard of quality, completeness, or performance.

Example

The brakes on Mizuki's car were found to be deficient during the safety inspection.

deficient in safety-related contexts

Yael argued that the company's emergency plan was deficient in several key areas.

Common collocations
  • deficient brakes
  • deficient planning
  • deficient training
  • deficient system
  • deficient performance
Synonyms
  • defective

    more specific — having a clear flaw or broken part

  • substandard

    below an expected or required level

  • flawed

    having imperfections or weaknesses

  • unsatisfactory

    not meeting expectations, broader in meaning

Antonyms

Grammar Patterns

deficient in + [noun/gerund]

be + deficient

Usage Note

Common in formal evaluations of quality, compliance, or performance. For everyday objects with physical flaws, 'defective' or 'faulty' is more natural. This sense also often appears in technical reports and official assessments.

Common Mistakes

This phone is deficient.
This phone is defective.
For everyday products with physical faults, use 'defective' or 'faulty'; 'deficient' sounds too formal and vague.

deficient — noun

Word family

Synonym discussion

Sense: adjective/1

All four words describe a shortfall, but they differ in tone and typical use. 'Deficient' carries a formal, often clinical or technical tone — it is the standard choice in medical reports ('iron-deficient'), nutritional science, and academic evaluations. 'Lacking' is the most flexible and conversational: you can say 'the soup lacks salt' in casual speech, which would sound odd with 'deficient'. 'Insufficient' focuses narrowly on quantity or degree, especially in formal or bureaucratic settings ('insufficient funds', 'insufficient evidence'). 'Inadequate' emphasises that something fails to meet a specific purpose or need, carrying a stronger evaluative judgment ('inadequate preparation for the exam'). For everyday contexts, use 'lacking'; for formal quantity problems, 'insufficient'; for failure to meet a standard, 'inadequate'; and for technical or essential shortfalls, 'deficient'.

deficient ↗lackinginsufficient ↗inadequate ↗

Common collocations

Adverbs

Prepositions

Etymology

LatinFrenchEnglish

From Latin 'deficientem', the present participle of 'deficere' (to fail, to be wanting), which was formed from 'de-' (down, away) and 'facere' (to do, to make). The sense was originally 'failing, lacking' in Late Latin, and entered English through Old French in the 1500s. The idea is of something that 'falls short' or 'fails to measure up'.