mother-out-law

mother-out-law (plural mothers-out-law)

1. Mother of one's boyfriend or girlfriend.
   • 2006, Harlyn Aizley, Confessions of the Other Mother: Nonbiological Lesbian Moms Tell All!‎ (Social Science), →ISBN, pZgDAQAAQBAJ, page 36:

     The old Cape Cod commune-istas had caught up enough with my mother out-law and were now asking after notable events in the lives of her offspring.

• mother-in-law

• brother-out-law
• daughter-out-law
• father-out-law
• sister-out-law
• son-out-law