fiber

noun

fi·​ber ˈfī-bər 

1

: a thread or a structure or object resembling a thread: such as

a(1)

: a slender root (as of a grass)

(2)

: an elongated tapering thick-walled plant cell void at maturity that imparts elasticity, flexibility, and tensile strength

b(1)

: a strand of nerve tissue : axon, dendrite

(2)

: one of the filaments composing most of the intercellular matrix of connective tissue

(3)

: one of the elongated contractile cells of muscle tissue

c

: a slender and greatly elongated natural or synthetic filament (as of wool, cotton, asbestos, gold, glass, or rayon) typically capable of being spun into yarn

d

: mostly indigestible material in food (such as legumes, whole grains, and vegetables) that stimulates the intestine to peristalsis and promotes elimination of waste from the large intestine : bulk, roughage

dietary fiber

trying to get more fiber in her diet

2

: material made of fibers

especially : vulcanized fiber

3

a

: an element that gives texture or substance

b

: basic toughness : strength, fortitude

c

: essential structure or character

the very fiber of a person's being

fibered

ˈfī-bərd 

adjective

Synonyms

• backbone
• courage
• grit
• stamina
• fortitude
• endurance
• spunk
• nerve
• determination
• intestinal fortitude
• bravery
• grittiness
• guts
• courageousness
• pluck
• constancy

Examples of fiber in a Sentence

It's important to get enough fiber in your diet.

What foods do you recommend as good sources of fiber?

foods that are high in fiber

The fabric is made from a mix of synthetic fibers.

The natural fibers allow the fabric to breathe.

The paper is made from both cotton and wood fiber.

Nylon is a very strong man-made fiber.

The police examined hair and bits of fiber found in the victim's car.

Recent Examples on the Web

That means cotton or linen fibers in loose, open weaves to maximize airflow and avoid trapping heat. —Amy Panos, Better Homes & Gardens, 20 July 2025

An ounce of cheese plus a few whole grain crackers also gives you protein and whole grains, which are high in fiber and contain calcium and several B vitamins. —Reyna Gobel, NPR, 19 July 2025

Chickpeas are rich in fiber, B vitamins, and magnesium, all of which contribute to better sleep quality and metabolic health. —Dr. Samanta Dall’agnese, CNBC, 18 July 2025

Bananas are a good source of fiber, vitamins, and minerals, especially potassium. —Amber J. Tresca, Verywell Health, 18 July 2025

Word History

Etymology

Middle French fibre, from Latin fibra

First Known Use

1607, in the meaning defined at sense 1

Phrases Containing fiber

• acrylic fiber
• bast fiber
• carbon fiber
• elastic fiber
• fiber-optic
• fiber optics
• glass fiber
• inter-fiber
• modacrylic fiber
• nerve fiber
• optical fiber
• Purkinje fiber
• vulcanized fiber
• with every fiber of one's being

Rhymes for fiber

• cyber
• fibre
• prescriber
• subscriber
• transcriber

Kids Definition

fiber

noun

fi·​ber ˈfī-bər 

1

: a thread or a structure or object resembling a thread: as

a

: a slender root (as of a grass)

b

: a long tapering thick-walled plant cell especially of vascular tissue

c

: a muscle cell

d

: axon, dendrite

e

: a slender and very long natural or synthetic unit of material (as wool, cotton, asbestos, gold, glass, or rayon) usually able to be spun into yarn

f

: mostly indigestible material in food that stimulates the intestine to move its contents along

called also bulk, roughage

2

: material made of fibers

3

: basic toughness : strength

moral fiber

Medical Definition

fiber

noun

fi·​ber

variants or chiefly British fibre

ˈfī-bər 

1

: a thread or a threadlike structure or object: as

a

: a strand of nerve tissue : axon, dendrite

b

: one of the filaments composing most of the intercellular matrix of connective tissue

c

: one of the elongated contractile cells of muscle tissue

2

: mostly indigestible material in food that stimulates the intestine to peristalsis

called also bulk, dietary fiber, roughage