- (often in the plural) A relative by marriage (or through affinity).
- Synonym: affine
- Sometimes specifically a parent-in-law of one's child, for which the dedicated terms co-mother-in-law, co-father-in-law are rare.
relative by marriage
parent-in-law of one's child
father-in-law — see father-in-law
mother-in-law — see mother-in-law