The parents of your live-in boyfriend/girlfriend.
I am having my sinlaws over for dinner...I hope I make a good impression since I have been shacking up with their son for a few weeks now and they are not down with the fact we are living in sin.
de PunTiff 01 August 2008
1 more definition
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.
de Jim Dempsey 28 August 2004