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"authenticity" is also used as a crossword clue. If that's what you saw, the answer is often realness (8 letters).
Definitions
The quality of being genuine, real, or trustworthy.
Word origin
From authentic + -ity.
Used in a sentence
“I hereby certify the authenticity of this copy.”
“The authenticity of this painting is questionable.”
Source: Wiktionary, CC BY-SA 4.0
Used as a crossword answer1 curated clues
01“Genuineness”12 letters
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