Expert gets fed up over time (4)
I believe the answer is:
deft
'expert' is the definition.
(thesaurus)
'fed up over time' is the wordplay.
'fed up' becomes 'def' ('fed' going up in a down clue).
'over' says to put letters next to each other.
'time' becomes 't'.
'def'+'t'='DEFT'
'gets' acts as a link.
(Other definitions for deft that I've seen before include "Handy" , "Adroit, dexterous" , "Handling things skilfully or neatly" , "Nimble-fingered" , "Adept" .)