Visit a small opera singer (6)
I believe the answer is:
callas
'opera singer' is the definition.
(I know this)
'visit a small' is the wordplay.
'visit' becomes 'call' (synonyms).
'small' becomes 's' (abbreviation - e.g. clothes size).
'call'+'a'+'s'='CALLAS'
(Other definitions for callas that I've seen before include "Superb soprano of Greek background" , "Arguably, the greatest diva of them all" , "Maria - - , opera singer" , "Maria, Greco-American soprano" , "Greek diva" .)