Lie about thread (5)
I believe the answer is:
fibre
'thread' is the definition.
(I've seen this in another clue)
'lie about' is the wordplay.
'lie' becomes 'fib' (fibbing is a kind of liing).
'about' becomes 're' ('re' means regarding or about).
'fib'+'re'='FIBRE'
(Other definitions for fibre that I've seen before include "Thread; stamina" , "Textile thread; roughage" , "Thread, strand" , "Threadlike substance" , "(Material composed of) thread(s)" .)