1560s, "incapable of being shaped," from un- (1) "not" + fashionable. Meaning "not in accordance with prevailing fashion" is attested from 1640s. Related: Unfashionably.
Entries linking to unfashionable
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.
fashionable adj.
c. 1600, "capable of being fashioned," also "conforming to prevailing tastes," from fashion + -able. From 1620s as "stylish;" as a noun, "person of fashion," from 1800. Related: Fashionably "in a manner accordant with fashion, custom, or prevailing practice; with modish elegance;" fashionably late is by 1809.
She was somewhat surprised, especially as she came fashionably late, to find in the drawing-room only old Mrs. Wynne, her nephew, and a lady, who from her dress and modest appearance was evidently nobody. [Maria Edgworth, "Tales of Fashionable Life," 1809]