son-in-law

[suhn-in-law]

noun

plural

sons-in-law 

1. the husband of one's child.

son-in-law

noun

1. the husband of one's daughter

Word History and Origins

Origin of son-in-law¹

First recorded in 1300–50; Middle English sone in lawe; son, in, law ¹; from Middle English in-lawe “in law,” i.e., “a person within the regulation and protection of the law,” based on the prohibition by Roman civil law and, later, Christian canon law, of marriages within four degrees of consanguinity, i.e., up to and including first cousins