English Reference
noun

fiber

n.
US /ˈfaɪbɝ/ fiber UK spelling fiber's, fiber's, fibre

  1. 01 B2 Upper Intermediate American English

    a single thin thread of a material like cotton, wool, or nylon.

    a single elongated piece of material, typically cylindrical, which can be spun into yarn or thread.

    Simple

    The detective found a tiny blue fiber from a sweater on the rug.

    In context

    Forensic analysts identified a synthetic fiber caught in the door frame that matched the specific blend used in the suspect's jacket.

    Usage

    Countable in this sense.

  2. 02 B2 Upper Intermediate American English Medicine

    the part of food, like vegetables and grains, that helps your body digest.

    indigestible carbohydrate derived from plants that aids in the passage of food through the digestive system.

    Simple

    You should eat more fruit and beans to get enough fiber in your diet.

    In context

    Nutritionists recommend a high-fiber diet to maintain gut health and reduce the risk of chronic metabolic diseases.

    Usage

    Usually uncountable when referring to the nutrient.

    roughagebulk
  3. 03 C1 Advanced American EnglishTechnical Science

    a long, thin cell in your body, such as in a muscle or nerve.

    an elongated, threadlike structure or cell found in animal or plant tissue.

    Simple

    The athlete suffered a tear in a muscle fiber during the race.

    In context

    Microscopic examination revealed that the nerve fibers were beginning to regenerate after the surgical intervention.

  4. 04 C2 Proficiency American EnglishLiterary

    the inner strength or character that makes a person do the right thing.

    the essential character, nature, or moral strength of a person.

    Simple

    Hard work and honesty were part of his moral fiber.

    In context

    The crisis tested the very fiber of her being, forcing her to choose between personal gain and ethical duty.

    Teacher's tip

    Often used in the fixed phrase 'moral fiber'.

  5. 05 C2 Proficiency American EnglishTechnical Computing

    a very light type of task that a computer program runs.

    a particularly lightweight thread of execution that uses cooperative rather than preemptive multitasking.

    Simple

    The programmer used a fiber to manage the background tasks efficiently.

    In context

    By implementing fibers instead of standard system threads, the application achieved higher concurrency with significantly lower memory overhead.

  6. 06 C2 Proficiency American EnglishTechnical Math

    a set of points that all map to the same result in a math function.

    the preimage of a single point under a given mapping or function.

    Simple

    We need to calculate the fiber of the function at this specific point.

    In context

    In algebraic geometry, the fiber of a morphism over a point provides crucial information about the structure of the map.

    preimage

Glass preforms are heated until their structure becomes loose enough to be drawn into extremely thin fibers.

ScienceDaily· 22 Aug 2026

Over two years, we used an old telecom fiber to record and identify 458 clear, high-quality thunderquakes.

The Conversation· 21 Aug 2026
This entry
Level B2 · Upper Intermediate
Frequency Common
Updated