Welcomed by mafioso, a thoughtful word (4)
I believe the answer is:
oath
'word' is the definition.
(thesaurus)
'welcomed by mafioso a thoughtful' is the wordplay.
'welcomed by' says the answer is hidden in the clue.
'OATH' is hidden in the letters of 'mafioso a thoughtful'.
(Other definitions for oath that I've seen before include "Vow or expletive" , "Strong language" , "A word with a witness" , "Swearword or solemn word" , "swearing" .)