Instrument for blokes, oddly unused (4)
I believe the answer is:
oboe
'instrument' is the definition.
(type of musical instrument)
'for blokes oddly unused' is the wordplay.
'oddly unused' means one should take alternating letters (letters in odd-numbered positions removed).
'for'+'blokes'='forblokes'
The alternating letters of 'forblokes' are 'OBOE'.
(Other definitions for oboe that I've seen before include "Producer of notes" , "Reed instrument" , "Double-reeded woodwind instrument" , "Instrument used in 1d" , "music producer" .)