Authenticity
Etymology
From Greek "authentikos" (original, genuine, principal), from "authentes" (one who does a thing himself — an author, master, even a perpetrator), combining "autos" (self) and a root meaning "to accomplish." The self-origination in that root is telling: the authentic is what comes from itself. Modern existentialist thought recast the word as a moral ideal of living from one’s own choices.
noun · /aw-then-TISS-uh-tee/
The quality of being true to one’s own character, values, and origins rather than to imposed expectations.
What it names
Reach for it to name fidelity to a real self or source — whether a person acting from their own convictions or an object being genuinely what it claims.
Example
The brand’s hunt for authenticity was undercut the moment the "candid" photos turned out to be staged.
Related idea
Sincerity is honesty toward others about what you feel; authenticity is fidelity to who you actually are — a shift the culture made when "know thyself" outranked "mean what you say." One can be sincere while conforming, but conformity is the enemy of authenticity.