fiber

American  

[fahy-ber] / ˈfaɪ bər /

especially British, fibre

noun

• fibers
  plural

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.

---

fiber British  

/ ˈfaɪbə /

noun

1. the usual US spelling of fibre

---

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.

---

Other Word Forms

Derived Forms

• fiberless
  adjective
• interfiber
  adjective

Inflected Forms

Nouns

• fibers
  plural

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

See Examples For:

fiber fibers

It says a prickly desert plant called hesperaloe produces fiber that can make stronger and softer paper products.

From The Wall Street Journal ● Aug. 4, 2026

An alternative to wood fiber would also be an environmental breakthrough.

From The Wall Street Journal ● Aug. 3, 2026

Corning has been betting that the massive infrastructure demands of AI will drive its next wave of growth, relying on its specialized optical fiber to link hyperscale data centers.

From The Wall Street Journal ● Jul. 28, 2026

The broadband market has gotten more crowded and more competitive, with the major wireless companies stepping up their investments in home-internet plans through both fiber offerings and fixed-wireless-access offerings that leverage their existing cellular networks.

From MarketWatch ● Jul. 24, 2026

In the pointed end of it, underneath the brown hairy-looking fiber, I saw what looked like two small black eyes and a tiny mouth.

From "Summer of the Monkeys" by Wilson Rawls

Still, they expressed hope that hesperaloe could help them reach a previously stated ambition to eventually stop using fibers from natural forests in their products.

From The Wall Street Journal ● Aug. 3, 2026

Over time, this can cause loss of strength, increased scarring, fat buildup within muscle tissue, and a decline in fast twitch fibers, which support rapid and powerful movements.

From Science Daily ● Jul. 24, 2026

This signal brings the cells out of their inactive state, allowing them to multiply, mature, and help rebuild damaged muscle fibers.

From Science Daily ● Jul. 24, 2026

To fire big ammunition, militaries need explosive chemicals derived from natural fibers that suddenly are in short supply.

From The Wall Street Journal ● Jul. 21, 2026

The fingertips of his right hand were pressed deeply into the soft fibers of the rug and his whole body vibrated from the wild pounding of his heart.

From "Native Son" by Richard Wright

Related Words

• grain
• thread
• tissue