Bar a learner for all time (5)
I believe the answer is:
lever
'bar' is the definition.
(lever is a kind of bar)
'a learner for all time' is the wordplay.
'a learner' becomes 'l'.
'for all time' becomes 'ever' (I've seen this before).
'l'+'ever'='LEVER'
(Other definitions for lever that I've seen before include "Bar for prising something" , "Prize" , "Exert pressure" , "Revel (anag.)" , "Jemmy" .)