Not seen or discovered; invisible. / Unskilled; inexperienced. / Not hitherto noticed; unobserved.

past participle of unsee

An examination involving material not previously seen or studied.

plural of unseen

(idiomatic) Not having seen the object beforehand.

Dated form of sight unseen.

Repulsive, disturbing, or horrific sights can never be erased from memory once they have been seen.

Alternative form of what has been seen cannot be unseen