fiber

American  

[fahy-ber] / ˈfaɪ bər /

especially British, fibre

noun

1. a fine, threadlike piece, as of cotton, jute, or asbestos.

2. a slender filament.

   a fiber of platinum.

3. filaments collectively.

4. matter or material composed of filaments.

   a plastic fiber.

5. something resembling a filament.

6. an essential character, quality, or strength.

   people of strong moral fiber.

7. Botany.

   1. filamentous matter from the bast tissue or other parts of plants, used for industrial purposes.

   2. a slender, threadlike root of a plant.

   3. a slender, tapered cell which, with like cells, serves to strengthen tissue.

8. Anatomy, Zoology. a slender, threadlike element or cell, as of nerve, muscle, or connective tissue.

9. Also called bulk, dietary fiber, roughage.  Nutrition.

   1. the structural part of plants and plant products that consists of carbohydrates, as cellulose and pectin, that are wholly or partially indigestible and when eaten stimulate peristalsis in the intestine.

   2. food containing a high amount of such carbohydrates, as whole grains, fruits, and vegetables.

10. Chemistry. vulcanized fiber.

11. Optics. optical fiber.

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fiber British  

/ ˈfaɪbə /

noun

1. the usual US spelling of fibre

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fiber Scientific  

/ fī′bər /

1. The parts of grains, fruits, and vegetables that contain cellulose and are not digested by the body. Fiber helps the intestines absorb water, which increases the bulk of the stool and causes it to move more quickly through the colon.

2. One of the elongated, thick-walled cells, often occurring in bundles, that give strength and support to tissue in vascular plants. Fibers are one type of sclerenchyma cell.

3. Any of the elongated cells of skeletal or cardiac muscle, made up of slender threadlike structures called myofibrils.

4. The axon of a neuron.

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Other Word Forms

• fiberless adjective
• interfiber adjective

Etymology

Origin of fiber

1350–1400; 1970–75 fiber for def. 9; Middle English fibre (< Middle French ) < Latin fibra filament

Explanation

Almost all fabrics, muscle structures, and even vegetables are composed of some sort of fiber, the noun meaning a long, thread-like substance. The word fiber is sometimes associated with moral character in a similar way that it is related to the physical material. The moral fiber of a person might be the thing that weaves together their character to make them the ethical (or unethical) person they are. For example, you might guess that the televangelist who asks for money from the elderly poor, but has a fancy sports car for every day of the week lacks moral fiber.

Example Sentences

And here, Orsolya’s sincere if haphazard search for understanding, visible in every fiber of Tompa’s affecting central performance, cleverly lets Jude expose the insufficiency in quick fixes.

From Los Angeles Times • Apr. 3, 2026

The system was tested both in laboratory fiber setups and across the University of Warsaw's existing fiber network over several kilometers.

From Science Daily • Apr. 1, 2026

The seeds also add a boost of fiber to your favorite sweet treats.

From Salon • Mar. 31, 2026

When you eat more vegetables “you increase your fiber, you feel full longer, and that helps mitigate the overeating from when you rely on ultraprocessed foods,” he said.

From The Wall Street Journal • Mar. 17, 2026

Every fiber of him was quivering and shaking.

From "The Martian Chronicles" by Ray Bradbury

Related Words

• grain
• thread
• tissue