1640s, from un- (1) "not" + past participle of convert (v.).
Entries linking to unconverted
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.
convert v.
c. 1300, "a change or turn from one religion to another," especially to Christianity, from Old French convertir "to turn around, turn towards; change, transform; convert, win over," from Vulgar Latin *convertire, from Latin convertere "turn around, transform," from assimilated form of com "with, together" (see con-) + vertere "to turn" (from PIE root *wer- (2) "to turn, bend").
The Latin verb was glossed in Old English by gecyrren, from cierran "to turn, return." General sense of "change into another form or substance, transmute" is from late 14c. Transitive sense of "turn from one use or destination to another" is from late 15c. Related: Converted; converting.