Stray fibres in underwear (6)
I believe the answer is:
briefs
'underwear' is the definition.
(I've seen this before)
'stray fibres' is the wordplay.
'stray' indicates an anagram.
'fibres' anagrammed gives 'BRIEFS'.
'in' acts as a link.
(Other definitions for briefs that I've seen before include "Garments" , "Underwear and lawyer's documents" , "They are prepared for barristers' perusal" , "Gives (someone) essential information" , "Documents stating facts and points of law" .)