1. a small or fine fiber or filament.
  2. Botany. any of the delicate hairs on the young roots of some plants.
  3. Cell Biology. any threadlike structure or filament.

noun plural -brils or -brillae (-ˈbrɪliː)

  1. a small fibre or part of a fibre
  2. biology a threadlike structure, such as a root hair or a thread of muscle tissue

1680s, back-formation from Modern Latin fibrilla, diminutive of Latin fibra (see fiber).


  1. A minute fiber.

  1. Any of various threadlike fibers or filaments that are constituent parts of a cell or larger structure. Cellulose fibrils are the main component of cell walls in plants. Fibrils make up the contractile part of striated muscle fiber in the body.
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