fibril (n.) Look up fibril at Dictionary.com
1680s, Anglicization of Modern Latin fibrilla "a little fiber, a filament," especially in botany, diminutive of Latin fibra "a fiber, filament" (see fiber). Latin fibra and fibrilla were used in 17c. physiology in English alongside nativized fibre and fibril. From 1931 as "thread-like molecular formation."