He can speak Italian or sing madly (6)
I believe the answer is:
signor
'he can speak italian' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'or sing madly' is the wordplay.
'madly' is an anagram indicator.
'or'+'sing'='orsing'
'orsing' anagrammed gives 'SIGNOR'.
Can you help me to learn more?
(Other definitions for signor that I've seen before include "Title of Italian-speaking man" , "Guy in Rome" , "Italian mister" , "Title of Italian man" , "Italian gentleman" .)