From step- + incest.
step-incest (uncountable)
- (informal) Sexual relations with a stepsibling.
2016 July 11, Michael Handelzalts, “Siblings Become Lovers in 'Billy & Billie'”, in Haaretz[1], Tel Aviv: Haaretz Daily Newspaper Ltd., →OCLC, archived from the original on 9 December 2023:With "Billy & Billie" LaBute makes his characters face the toil and trouble of a budding relationship, while struggling to carry the additional burden of a very deep-seated taboo of incest, even if it is step-incest.
2023 December 7, Jessica Stoya, Rich Juzwiak, quoting Jessica Stoya, “When It Comes to Sex, I’m Afraid I’ve Become the Creepy Old Man. I Can’t Help It.”, in Slate[2], New York, N.Y.: The Slate Group, →ISSN, →OCLC, archived from the original on 2023-12-08:So I don't want to just send our LW off to Google MILFs. I think if he already feels weird, step-incest is going to make him feel so much weirder.
