Learning to recognise advantage getting over fifty (9)
I believe the answer is:
knowledge
'learning' is the definition.
(thesaurus)
'recognise advantage getting over fifty' is the wordplay.
'recognise' becomes 'know' ('know' can be a synonym of 'recognize'**).
'advantage' becomes 'edge' (edge is a kind of advantage).
'getting' says to put letters next to each other.
'over' indicates putting letters inside.
'fifty' becomes 'l' ('L' can be a synonym of 'fifty').
'know'+'edge'='knowedge'
'knowedge' going around 'l' is 'KNOWLEDGE'.
'to' acts as a link.
(Other definitions for knowledge that I've seen before include "Information gained by learning" , "Grasp" , "Cognition, wisdom" , "Information - erudition" , "The result of perception, learning and reasoning" .)