A base retrieved this truant? (4)
I believe the answer is:
awol
'this truant?' is the definition.
(I've seen this before)
'a base retrieved' is the wordplay.
'base' becomes 'low' (synonyms).
'retrieved' shows that the letters should be reversed in order.
'low' in reverse letter order is 'wol'.
'a'+'wol'='AWOL'
(Other definitions for awol that I've seen before include "Truant (or just missing)" , "Absent without leave (abbr.)" , "Take unofficial leave (abbrev.)" , "On the lam" , "Not present when supposed to be" .)