Hothead joins American company - he's married, of course (7)
I believe the answer is:
husband
'hothead joins american company he's married of course' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'hothead joins american company he's' is the wordplay.
'hothead' becomes 'h' (head letter of 'hot').
'joins' is a charade indicator (letters next to each other).
'american' becomes 'us' (abbreviation for United States).
'company he's' becomes 'band' (I am not sure about this - if you are sure you should believe this answer much more).
'h'+'us'+'band'='HUSBAND'
Can you help me to learn more?
(Other definitions for husband that I've seen before include "Woman's matrimonial partner" , "be economical" , "Economically manage" , "Use economically - partner" , "Use (resources) thriftily" .)