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"unseen" is also used as a crossword clue. If that's what you saw, the answer is often undetected (10 letters).
Definitions
Not seen, noticed, or previously observed.
Word origin
From Middle English unsen, unseyn, unseien, from Old English unġesewen, from Proto-Germanic *unsewanaz, equivalent to un- + seen. Cognate with Dutch ongezien (“unseen”), German Low German unsehn (“unseen”), German ungesehen (“unseen”).
Used in a sentence
“You became to me the visible incarnation of that unseen ideal whose memory haunts us artists like an exquisite dream.”
“When night had fallen, the she-demon stole forth toward the hall, which she entered unheard and unseen.”
“I to the world am like a drop of water That in the ocean seeks another drop, Who, falling there to find his fellow forth, Unseen, inquisitive, confounds himself.”
Source: Wiktionary, CC BY-SA 4.0
Used as a crossword answer2 curated clues
01“Hidden from view”6 letters
02“Not visible”6 letters
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