in-law; relative by marriage
Refers to relatives connected through marriage, such as a spouse's family. Often used in formal or legal contexts.
The in-law relationships are complicated, and at family gatherings I lose track of who is who.
relation by marriage; affinity
Compound of 姻 (marriage) and 戚 (relative), both kanji carrying the sense of kinship through marriage. The reading is on'yomi.