Wager about a pound (4)
I believe the answer is:
beat
'pound' is the definition.
(synonyms)
'wager about a' is the wordplay.
'wager' becomes 'bet' (synonyms).
'about' means one lot of letters goes inside another.
'bet' going around 'a' is 'BEAT'.
(Other definitions for beat that I've seen before include "Strike; rhythm" , "Policeman's route; strike" , "course run regularly" , "buffet" , "Get the better of in competition" .)