Learner always needing time to gain advantage (8)
I believe the answer is:
leverage
'advantage' is the definition.
(I know that leverage is a type of advantage)
'learner always needing time' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'always' becomes 'ever' (synonyms).
'needing' means one lot of letters go next to another.
'time' becomes 'age' (an age is a period of time).
'l'+'ever'+'age'='LEVERAGE'
'to gain' acts as a link.
(Other definitions for leverage that I've seen before include "Power of achievement; (US) gearing" , "can achieve power" , "financial advantage" , "Power to act effectively" , "Capacity to exert pressure" .)