A learner, in past, with skill (4)
I believe the answer is:
ably
'with skill' is the definition.
(I've seen this before)
'a learner in past' is the wordplay.
'learner' becomes 'l'.
'in' indicates putting letters inside.
'past' becomes 'by' ('by' can be a synonym of 'past').
'l' placed into 'by' is 'bly'.
'a'+'bly'='ABLY'
(Other definitions for ably that I've seen before include "With competence" , "Masterfully" , "In capable manner" , "In a competent fashion" , "well" .)