Left to get master (5)
I believe the answer is:
learn
'master' is the definition.
(thesaurus)
'left to get' is the wordplay.
'left' becomes 'l' (common abbreviation).
'to get' becomes 'earn' (earning is a kind of getting).
'l'+'earn'='LEARN'
(Other definitions for learn that I've seen before include "Get to know" , "Study or digest" , "be taught a lesson" , "Renal (anag)" , "Ascertain" .)