mid-14c., from un- (1) "not" + past participle of sell (v.).
Entries linking to unsold
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.
sell v.
Middle English sellen, from Old English sellan "to give (something to someone), furnish, supply, lend; surrender, give up; deliver to; promise," from Proto-Germanic *saljanan "offer up, deliver" (source also of Old Norse selja "to hand over, deliver, sell;" Old Frisian sella, Old High German sellen "to give, hand over, sell;" Gothic saljan "to offer a sacrifice"), ultimately from PIE root *sel- (3) "to take, grasp."
Meaning "to give up for money, accept a price or reward for" had emerged by late Old English, but in Chaucer selle still can mean "to give." Students of Old English learn early that the word they encounter that looks like sell usually means "give." An Old English word for "to sell" was bebycgan, from bycgan "to buy."
The meaning "betray for gain" is from c. 1200. Slang meaning "to swindle" is from 1590s. To sell off "dispose of by sale, sell all of" is by 1700. To sell one's soul "make a contract with the devil," often figurative, is from c. 1570. Sell-by in reference to dates stamped on perishable packaged foods is from 1972. To sell like hot cakes is from 1839. To sell (someone) down the river figuratively is by 1927, probably from or with recollection of slavery days, on notion of sale from the Upper South to the cotton plantations of the Deep South (attested in this literal sense since 1851).