1.
bridegroom, groom
A man who is getting married or has just married.
2.
son-in-law
The husband of one's daughter. Also used for a man who marries into and takes his wife's family name.
Usage
When referring to someone else's son-in-law or groom politely, お婿さん is used. 婿養子 specifically refers to a man who marries into his wife's family and takes her surname — a practice with deep roots in Japanese family law and tradition.
The expression 婿を取る means to take in a son-in-law (i.e., to have a man marry into the family).