Vagrant, male lying in bunker (5)
I believe the answer is:
tramp
'vagrant' is the definition.
(thesaurus)
'male lying in bunker' is the wordplay.
'male' becomes 'm' (common abbreviation).
'lying in' means one lot of letters goes inside another.
'bunker' becomes 'trap' ('trap' can be a synonym of 'bunker').
'm' inserted inside 'trap' is 'TRAMP'.
(Other definitions for tramp that I've seen before include "Footslog" , "Go heavily" , "man down on his luck" , "Vagrant - cargo ship" , "cargo-boat" .)