Certainly beyond yours truly, a limit (7)
I believe the answer is:
measure
'limit' is the definition.
(thesaurus)
'certainly beyond yours truly a' is the wordplay.
'certainly' becomes 'sure' (synonyms).
'beyond' says to put letters next to each other.
'yours truly' becomes 'me' (the person who set this crossword).
'me'+'a'='mea'
'sure' after 'mea' is 'MEASURE'.
(Other definitions for measure that I've seen before include "Get hands, perhaps" , "Find the dimensions" , "capacity" , "Portion" , "Take size of" .)