Filament (6)
'filament' is the definition.
(I know that filament can be written as strand)
This is all the clue.
(Other definitions for strand that I've seen before include "Piece of yarn etc - London street" , "Line of fibres twisted to form a thread" , "A thread or a beach" , "Beach or single hair" , "Leave helpless - single thread" .)
(Other definitions for thread that I've seen before include "Subject" , "Fine strand" , "Train of thought - screw feature" , "Cord - Internet chat room discussion" , "Sewing chord" .)
'filament' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for fibre that I've seen before include "Thread, strand" , "Brief (anag.)" , "Long fine thread" , "Basis of yarn" , "In brief, a thread" .)