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

Derived 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

Connectivity has become the latest frontier amid the AI infrastructure buildout and fiber optics are replacing copper for long-distance and rack-to-rack interconnects in AI data centers.

From The Wall Street Journal • Jun. 2, 2026

In addition to vitamin C, guava also provides vitamin A, folate, dietary fiber, and small amounts of iron.

From Science Daily • May 27, 2026

It expects the Malaysian telecommunications company’s revenue and Ebit to maintain single-digit growth, driven by stronger enterprise demand in 2H and stable income from fiber service.

From The Wall Street Journal • May 22, 2026

Somewhere around 95% of Americans don’t eat enough fiber.

From MarketWatch • May 19, 2026

His own was the flimsiest cotton, and tender in every fiber from long wear.

From "The Golden Goblet" by Eloise Jarvis McGraw

Related Words

• grain
• thread
• tissue