Stand-up artist perhaps of vast size hasn't succeeded (5)
I believe the answer is:
comic
'stand-up artist perhaps' is the definition.
'of vast size hasn't succeeded' is the wordplay.
'of vast size' becomes 'cosmic'.
'hasn't' is a deletion indicator.
'succeeded' becomes 's' (genealogical abbreviation).
'cosmic' with 's' taken out is 'COMIC'.
(Other definitions for comic that I've seen before include "Funny, droll" , "Droll - comedian" , "Funny (person, paper)" , "Funny man, may be stand-up" , "Children's publication" .)