Onecest 

A word used by The Lorax fandom for the pairing between the Once-ler and the Greed-ler.

Person1: ''The Onceler and the Greedler are the same person, though.''
Person 2: ''I know, it's kinda like a guy dating his own brother, the fandom calls it onecest.''

Onecest by nini21 November 9, 2012

Oncest 

When the two versions of the main antagonist (The Onceler) in the Dr. Seuss book, The Lorax, are having sexual intercourse with each other.

I, the creator of this definition, had recently found oncest fanart on my TikTok For You Page because once my friend sent me a video as a joke and now it's all over my For You Page. I was so disturbed, I cried into a piece of stale bread.

Oncest by XAXAXAXXAXAXXAXAXAXXAXA June 18, 2023

One-cest 

When the die hard kingdom hearts fans ship together the characters Sora, Roxas, and Ventus.

"What the fuck is this One-cest? You can't make Sora, Roxas, and Ventus have a threesome. They're the same person!"

One-cest by I'm going to Kashoot myself January 7, 2019

oncest 

slang for "once"

Would you do as I tell you for oncest!

oncest by aarby08808 February 4, 2018

oncest 

when your on top of your family memebers but not fucking them

“that’s incest”
“no that’s oncest”

oncest by bitchybitch29 July 4, 2020

oncest 

when one sibling is on top of the other

this isnt incest, this is oncest.

oncest by hoepp69 July 4, 2020