Frequently, in poetry (3)
I believe the answer is:
'frequently in poetry' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for oft that I've seen before include "Many times, of old" , "Many a time to the poet." , "Many times (archaic)" , "''... in the stilly night'' (Moore melody)" , "Quite frequently, according to the poet" .)