Origin and history of unproved

c. 1200, prēven, pruven, proven "to try by experience or by a test or standard; evaluate; demonstrate in practice," from Old French prover, pruver "show; convince; put to the test" (11c., Modern French prouver), from Latin probare "to make good; esteem, represent as good; make credible, show, demonstrate; test, inspect; judge by trial" (source also of Spanish probar, Italian probare, and English probe), from probus "worthy, good, upright, virtuous."

This is from PIE *pro-bhwo- "being in front," from *pro-, extended form of root *per- (1) "forward," hence "in front of," + root *bhu- "to be," source also of Latin fui "I have been," futurus "about to be;" Old English beon "to be;" see be.

From early 13c. as "render certain, put out of doubt," also "establish the validity or authenticity of a will, etc." By c. 1300 as "test and find worthy, virtuous, false, etc.," also "find out, discover, ascertain; prove by argument." By mid-14c. as "check the accuracy of." The meaning "be found to be (a hero, coward, etc.) by experience or trial" is by late 14c.

The word had many more senses and broader application in Middle English than Modern English: "to experience; to strive, endeavor; act, accomplish; thrive, succeed." Also in Middle English in a now-obsolete sense of "approve, sanction, praise" (c. 1300; compare approve). Related: Proved; proven; proving. Proving ground "place used for firing cannons for making ballistics tests and testing powder" is by 1837.

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."

The most prolific of English prefixes, freely and widely used in Old English, where it forms more than 1,000 compounds. 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.

Often euphemistic (untruth for "a lie") or emphatic, if there is a sense already of divestment or releasing: unpeel " to peel;" unpick "pick (a lock) with burglars' tools;" unloose for "to loosen."

It also makes words from phrases, such as uncalled-for, c. 1600; undreamed-of, 1630s. Fuller (1661) has unbooklearned. A mid-15c. description of a legal will has unawaydoable; Ben Jonson has un-in-one-breath-utterable. The word uncome-at-able is attested by 1690s in Congreve, frowned at by Samuel Johnson in the 18th century and by Fowler in the 20th ("The word had doubtless, two or three centuries ago, a jolly daredevil hang-the-grammarians air about it ; that has long evaporated ; it serves no purpose that inaccessible does not ....").

But the practice continued; unlawlearned (Bentham, 1810), unlayholdable (1860); unputdownable, of a book, is by 1947; unpindownable, by 1966. Also compare put-up-able-with (1812). As a prefix in telegraphese, to replace not and save the cost of a word, it is attested by 1936.

With the variety of its possible use, and the need for negatives, the number of un- words that might be made in English is almost endless, and that some are used and some never is owing to the caprice of authors.

Dictionary editors noted this since 18c. but also padded the list. John Ash's "New and Complete Dictionary of the English Language" (1775) has many pages of one-line un- entries; among a dozen consecutive entries are unhaggled, unhaired, unhalooed, unhaltering (adj.), unhaltering (n.), which sorts of words OED (1989) notes were "obviously manufactured for the purpose" and some turn up in other texts only decades later, if at all. (Ash vindicated.)