Reportedly, underground worker's petty (5)
I believe the answer is:
minor
'petty' is the definition.
(thesaurus)
'reportedly underground worker's' is the wordplay.
'reportedly' shows a homophone (sound like).
'underground worker' becomes 'miner' (I've seen this before).
'miner' is a homophone of 'MINOR'.
(Other definitions for minor that I've seen before include "Morris car; tending to melancholy (mus.)" , "Of less importance" , "Of small importance" , "One hasn't reached legal majority" , "Adolescent" .)