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

Manufacturers counter with front-of-the-package labeling that highlights added vitamins and minerals or the “heart healthy” benefits of supplied fiber.

From The Wall Street Journal ● Sep. 17, 2026

Once the yeast-derived ingredients have been produced, researchers combine them with fiber, starch, and sweetener.

From Science Daily ● Sep. 13, 2026

Verizon VZ 0.73%increase; green up pointing triangle and Corning reached a multibillion-dollar agreement to deploy more than 80 million miles of high-density optical fiber across the nation over the coming five years.

From The Wall Street Journal ● Sep. 8, 2026

Often times, data centers need to sit close to power substations and fiber lines, which often means edging up against suburbs and exurbs where people already live.

From MarketWatch ● Sep. 4, 2026

To have such a deep taproot in a single place, to be immersed in it so thoroughly that it had steeped into every fiber of your being: she couldn’t imagine it.

From "Little Fires Everywhere" by Celeste Ng

Superficial white matter forms a thin layer of nerve fibers directly beneath the gray matter covering the outside of the brain.

From Science Daily ● Sep. 14, 2026

Natural fibers like cotton, cashmere and silk feature prominently in its clothes, a departure from other midmarket retailers that have turned to cheaper synthetics.

From The Wall Street Journal ● Sep. 10, 2026

Their brightness comes from light scattering off the exposed fibers of the traditional washi paper.

From Science Daily ● Sep. 10, 2026

Crews have already covered the fragile area with 4,500 linear feet of wattles, long tubes whose natural fibers hold soil in place, the National Park Service said.

From Los Angeles Times ● Sep. 2, 2026

If you ever eat cattails, be sure to cook them well, otherwise the fibers are tough and they take more chewing to get the starchy food from them than they are worth.

From "My Side of the Mountain" by Jean Craighead George

Related Words

• grain
• thread
• tissue