Ernie's funny girl (5)
I believe the answer is:
irene
'girl' is the definition.
(I've seen this before)
'ernie's funny' is the wordplay.
'funny' indicates an anagram.
'ernie' anagrammed gives 'IRENE'.
(Other definitions for irene that I've seen before include "- - Handl, actress" , "Peaceful girl" , "Greek goddess of peace (English name)" , "Girl's name (meaning Peace)" , "Goddess of peace - Byzantine ruler" .)