Pitman sounds unimportant (5)
I believe the answer is:
miner
'pitman' is the definition.
(I've seen this before)
'sounds unimportant' is the wordplay.
'sounds' indicates a 'sounds like' (homophone) clue.
'unimportant' becomes 'minor' (I've seen this in another clue).
'minor' sounds like 'MINER'.
(Other definitions for miner that I've seen before include "Underground labourer" , "One works underground" , "One sent down for work" , "Person who works underground" , "Bevin boy" .)