fiber

fiber — noun

1. a very thin strand of material that comes from plants, animals, or is made by hu

1.nounB1
Definition

a very thin strand of material that comes from plants, animals, or is made by humans, used to create threads, fabrics, ropes, and other products.

Example

Cotton fiber is soft and breathable, making it ideal for summer clothing.

material use: cotton fiber + adjective describing quality

The jacket is made from recycled synthetic fibers that keep out the wind.

Common collocations
  • synthetic fiber
  • natural fiber
  • cotton fiber
  • carbon fiber
  • plant fiber
  • glass fiber
Synonyms
  • thread

    a thin strand of fibers twisted together for sewing, not the raw individual strand

  • filament

    a very fine single strand, often used for synthetic or natural single fibers like silk

  • strand

    a single thin piece of something like hair, wire, or fiber, but not a material category

Usage Note

Fiber is both countable (referring to individual strands) and uncountable (referring to the material as a whole). The British spelling is 'fibre'.

Common Mistakes

I bought some cotton threads to make a shirt.
I bought some cotton fiber to make a shirt.
Fiber is the raw material; thread is made from twisted fibers for sewing.
The rope is made of strong threads.
The rope is made of strong fibers.
Fibers are twisted into yarn, and yarn is twisted into rope; use 'fiber' for the base material.

2. parts of plants that your body cannot digest but that help food move through you

2.nounB1
Definition

parts of plants that your body cannot digest but that help food move through your digestive system, keeping your digestion healthy.

Example

Eating more fiber can help your digestive system work more smoothly.

uncountable: eat more fiber

Linh added beans and oats to her breakfast to increase her fiber intake.

Common collocations
  • dietary fiber
  • soluble fiber
  • insoluble fiber
  • high-fiber foods
  • fiber intake
  • fiber content
Synonyms
  • roughage

    an older, less common term for dietary fiber, especially in British English

  • bulk

    refers to the physical volume fiber adds to digested food, not the fiber itself

Usage Note

Primarily uncountable — you cannot say 'a fiber' to mean dietary fiber. Also called 'roughage' or 'bulk' in older textbooks.

Common Mistakes

I need more fibers in my diet.
I need more fiber in my diet.
Dietary fiber is uncountable; do not add -s.

3. a thin, thread-shaped cell in the body, especially the cells that make up muscle

3.nounB2
Definition

a thin, thread-shaped cell in the body, especially the cells that make up muscles or carry signals along nerves.

Example

Each muscle fiber contracts when it receives a signal from the nerves.

countable: each muscle fiber + verb of action

The accident damaged several nerve fibers in Mathieu's right hand, reducing his sense of touch.

Common collocations
  • muscle fiber
  • nerve fiber
  • skeletal muscle fiber
  • nerve fiber bundle
Synonyms
  • myocyte

    the technical scientific name for a muscle cell; very formal, only used in specialist contexts

  • neurite

    a general term for any projection from a nerve cell body, including axons and dendrites; highly technical

Usage Note

Almost always used in the plural when referring to collections ('muscle fibers', 'nerve fibers'). The singular form usually appears in technical descriptions ('a single muscle fiber').

Common Mistakes

He pulled a fiber in his leg.
He pulled a muscle fiber in his leg.
A 'muscle fiber' is a specific type of cell; 'fiber' alone in this context is ambiguous.

4. the courage and determination to do what is morally right, especially when facin

4.nounC1
Definition

the courage and determination to do what is morally right, especially when facing pressure to do something wrong or dishonest.

Example

Camila showed great moral fiber by telling the truth even when it hurt.

collocation: moral fiber + show great [quality]

Cyrus showed real moral fiber by admitting he had made the error, even though it cost him his bonus.

show moral fiber + admit error + consequence

Common collocations
  • moral fiber
  • inner fiber
  • moral fiber of [someone/something]
Synonyms
  • fortitude

    courage in pain or adversity; more general than moral fiber, which is specifically about moral choices

  • backbone

    informal synonym for moral strength; 'to have backbone' means having courage to stand up for what is right

  • integrity

    the quality of being honest and having strong moral principles; broader, not limited to difficult situations

Antonyms
  • cowardice

    lack of courage to face danger or difficulty, opposite of moral strength

  • weakness

    lack of moral firmness or resolve

Usage Note

Almost always appears with 'moral' before it ('moral fiber'). The word 'fiber' alone in this sense is rare and would sound old-fashioned. Do not use to describe physical toughness or endurance — that meaning does not exist.

Common Mistakes

She has strong fiber after years of training at the gym.
She has strong muscles after years of training at the gym.
'Fiber' for moral strength only; do not use it for physical strength.
His fiber helped him run the marathon.
His moral fiber helped him keep going when he wanted to quit.
Always pair with 'moral' to make the figurative meaning clear.

Word family

  • fibrous
    adjectiveB2
  • fiberglass
    nounB2
  • fiber-optic
    adjectiveC1
  • fiberboard
    nounC1

Synonym discussion

Sense: noun/1

All four words describe long, thin objects, but they differ in how they are used. A 'fiber' is the basic building block — the raw, individual strand from plants, animals, or synthetic sources. A 'thread' is made by twisting two or more fibers together for sewing or weaving. 'Yarn' is a thicker, continuous strand of twisted fibers used for knitting or crocheting, often made of wool or cotton. A 'filament' is an extremely fine single fiber, often used in technical or scientific contexts, such as the filament of a light bulb or a spider's silk. A 'strand' is a single piece of something long and thin, like a strand of hair, wire, or rope. For example: 'Cotton fiber is spun into thread,' but 'She knitted a scarf with soft wool yarn.'

thread ↗yarn ↗filamentstrand ↗

Common collocations

Nouns

  • fiber content
  • fiber type
  • fiber structure
  • fiber strength

Phrases

  • rich in fiber
  • high in fiber
  • made of fiber

Prepositions

  • fiber from [source]
  • fiber in [food/material]

Etymology

LatinFrenchEnglish

The word comes from Latin 'fibra' meaning a thread or filament. It entered French as 'fibre' and then into English in the 1300s, originally referring to plant or animal threads. The figurative meaning of moral strength or character developed in the early 1800s. The modern American spelling 'fiber' follows the general English pattern of -re to -er (like 'center' from 'centre').