Married, is son with American wife? (6)
I believe the answer is:
missus
'wife?' is the definition.
(informal term for someone's wife)
'married is son with american' is the wordplay.
'married' becomes 'm' (abbreviation, e.g. in genealogy).
'son' becomes 's' (genealogical abbreviation for son).
'with' means one lot of letters go next to another.
'american' becomes 'US' (United States).
'm'+'is'+'s'+'us'='MISSUS'
(Other definitions for missus that I've seen before include "The old lady" , "Wife (colloquial)" , "Dutch American" , "As partner" , "Wife (informal)" .)