c. 1600, from un- (1) "not" + past participle of meet (v.).
Entries linking to unmet
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.
meet v.
Middle English mēten, from Old English metan "to find, find out; fall in with, encounter, come into the same place with; obtain," from Proto-Germanic *motjanan (source also of Old Norse mæta, Old Frisian meta, Old Saxon motian "to meet," Gothic gamotijan), from PIE root *mod- "to meet, assemble." Related to Old English gemot "meeting."
By c. 1300, of things, "to come into physical contact with, join by touching or uniting with;" also, of persons, "come together by approaching from the opposite direction; come into collision with, combat." Abstractly, "to come upon, encounter (as in meet with approval, meet one's destiny) by late 14c. Sense of "come into conformity with, be or act in agreement with" (as in meet expectations) is by 1690s.
Intransitive sense, of people, "to come together" is from mid-14c.; of members of an organized body or society, "to assemble," by 1520s. Related: Met; meeting. To meet (someone) halfway in the figurative sense "make mutual and equal concessions to" is from 1620s. Well met as a salutation of compliment is by mid-15c.