Parade one month ago (5,4)
I believe the answer is:
march past
'parade' is the definition.
(thesaurus)
'one month ago' is the wordplay.
'one month' becomes 'march' (March is an example).
'ago' becomes 'past' ('past' can be similar in meaning to 'ago').
'march'+'past'='MARCH PAST'
(Other definitions for march past that I've seen before include "Army manoeuvre" , "Companion" , "in previous tax year?" , "Movement of a body of soldiers being reviewed" , "Parade before a saluting base" .)