sin-law

The parent of a partner in a romantic and cohabitating but unmarried relationship.

Sadly, John's sin-laws dropped by the house for Jane's birthday.

by Jim Dempsey August 28, 2004

Sin-in-law

The relationship a boyfriend has to his live-in-girlfriend's parents.

Girlfriend: Mom, Andrew and I are moving in together

Mom: Oh, you're going to live together before marriage? Great, how I've always wanted a SIN-IN-LAW.

Girlfriend: But we love each other!

Mom: That's great, your love can help keep you warm right alongside the BURNING FIRES OF ETERNAL DAMNATION

by green duck butter November 21, 2016