American shot past (3)
I believe the answer is:
ago
'past' is the definition.
(similar in meaning)
'american shot' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'shot' becomes 'go' (both can mean an attempt).
'a'+'go'='AGO'
(Other definitions for ago that I've seen before include "Previously" , "Earlier, gone by" , "Time past" , "Back (in time)" , "In past times" .)