Drive, say, all but disappeared (3,2)
I believe the answer is:
egg on
'drive' is the definition.
(thesaurus)
'say all but disappeared' is the wordplay.
'say' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'all but' means to remove the last letter ('all but' can mean 'almost' or 'nearly').
'disappeared' becomes 'gone' (going is a kind of disappearing).
'gone' with its final letter removed is 'gon'.
'eg'+'gon'='EGG ON'
(Other definitions for egg on that I've seen before include "Urge (someone) to take risks" , "this face is obvious embarrassment" , "Urge, impel" , "Fire" , "One cooking breakfast might have this" .)