Wager about sick quarters (6)
I believe the answer is:
billet
'quarters' is the definition.
(I've seen this in another clue)
'wager about sick' is the wordplay.
'wager' becomes 'bet' (synonyms).
'about' means one lot of letters goes inside another.
'sick' becomes 'ill' (similar in meaning).
'bet' going around 'ill' is 'BILLET'.
(Other definitions for billet that I've seen before include "Job" , "Soldier's lodgings" , "Lodgings for troops in private house" , "Piece of wood - bar of metal - place to stay" , "Place for a soldier to stay" .)