noun
relation by marriage; affinity
Refers to family ties created through marriage, as opposed to blood relations. Often used in formal or legal contexts.
彼とは姻戚関係にある。
I am related to him by marriage.
姻戚関係を図にまとめた。
I made a diagram of the relations by marriage.
血縁関係 refers to blood relations, while 姻戚関係 refers to relations through marriage.
Compound of 姻戚 (in-law, marriage relation) and 関係 (relation). The exact historical derivation is uncertain, but the kanji 姻 and 戚 both relate to marriage and kinship.