Wearing away with time, certainly (7)
I believe the answer is:
erasure
'wearing away' is the definition.
(thesaurus)
'with time certainly' is the wordplay.
'with' means one lot of letters go next to another.
'time' becomes 'era' (an era is a period of time).
'certainly' becomes 'sure' (synonyms).
'era'+'sure' is 'ERASURE'.
(Other definitions for erasure that I've seen before include "Rubbing out - English synthpop duo" , "Process of rubbing out" , "Censorship" , "Band with Andy Bell and Vince Clarke, or wipe-out" , "group from the 80s" .)