1720, from un- (1) "not" + past participle of notice (v.).
Entries linking to unnoticed
un- 1
prefix of negation, Old English un-, from Proto-Germanic *un- (source also of Old Saxon, Old Frisian, Old High German, German un-, Gothic un-, Dutch on-), from PIE *n- (source of Sanskrit a-, an- "not," Greek a-, an-, Old Irish an-, Latin in-), combining form of PIE root *ne- "not." Often euphemistic (such as untruth for "lie").
The most prolific of English prefixes, freely and widely used in Old English, where it forms more than 1,000 compounds. It underwent a mass extinction in early Middle English, but emerged with renewed vigor 16c. to form compounds with native and imported words. It disputes with Latin-derived cognate in- (1) the right to form the negation of certain words (indigestable/undigestable, etc.), and though both might be deployed in cooperation to indicate shades of meaning (unfamous/infamous), typically they are not.
It also makes words from phrases (such as uncalled-for, c. 1600; undreamed-of, 1630s; uncome-at-able, 1690s; unputdownable, 1947, of a book; un-in-one-breath-utterable, Ben Jonson; etc., but the habit is not restricted to un-; such as put-up-able-with, 1812). As a prefix in telegramese to replace not and save the cost of a word, it is attested by 1936.
notice v.
early 15c., "to notify, give notice of" (a sense obsolete since 17c.), from notice (n.). The sense of "to point out, refer to, remark upon" is from 1620s. The meaning "to take notice of, perceive, become aware of" is attested by 1757, but it was long execrated by purists in England as an Americanism (also occasionally as a Scottishism, the two offenses not being clearly distinguished). Ben Franklin noted it as one of the words (along with verbal uses of progress and advocate) that seemed to him to have become popular in America while he was absent in France during the Revolution. Related: Noticed; noticing.