Deadass
Etymology
African American Vernacular English, strongly associated with New York City, from “dead ass” meaning completely serious (with “dead” as an intensifier, as in “dead serious”). It spread nationally through NYC rap and social media in the 2010s.
adverb · /DED-ass/
Seriously, genuinely, for real — used to insist you mean exactly what you just said.
What it names
It pre-empts disbelief: you flag a statement as sincere before the listener can take it as a joke or an exaggeration. It also stands alone as a question — “deadass?” — meaning “are you serious?”
Example
I’m deadass going to quit if they cancel the remote days.
Related idea
A companion to no cap: both assert honesty, but no cap denies that you’re lying while deadass affirms that you’re serious.