Definition of "in-law"

in-law

noun
plural in-laws
1. (often in the plural) A relative by marriage (or through affinity).
  Quotations
  Louie: 'Neither boiling nor baking can diminish this creature's overpowering musky scent. Only suitable for serving to unpleasant in-laws.'
  2004, Nintendo EAD, Pikmin 2, Nintendo, level/area: Piklopedia
2. 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.