There is a short poem titled “Gloss” by David McCord, written to draw attention to English words that appear to be antonyms of words that don’t exist. It goes like this:
I know a little man both ept and ert. An intro-? extro-? No, he's just a vert. Sheveled and couth and kempt, pecunious, ane, His image trudes upon the ceptive brain.
When life turns sipid and the mind is traught, The spirit soars as I would sist it ought. Chalantly then, like any gainly goof, My digent self is sertive, choate, loof.
Which of those root words have been simply lost to history, and which never existed? You can have a word that starts with dis- and isn’t an antonym, e.g. “distance”, is that the case with any of these words?
- (in)ept - Direct from the Latin ineptus, although thanks to Latin's complicated rules, the opposite was aptus, which survives in the English word "apt" (and aptitude and adapt and others).
- (in)ert - Like inept, this comes from the Latin, in this case inertem. The non-negative version artem became "art".
- (intro/extro)vert - The second half comes from the Latin vertere (to turn), and is the source of the word "versus".
- (di)sheveled - This word originally meant "bare-headed", from the Old French des- and chevel (hair).
- (un)couth - In Old English, this meant "unknown", the negation of the root cuð, the past participle of the word cunnan meaning "to know". It is also related to "can" (in the sense of being able to do something) and "could" and "cunning".
- (un)kempt - Kempt is certainly less common, but it's far from dead.
- (im)pecunious - Direct from the Latin. The root word pecunia is also the source of the English "pecuniary".
- (in)ane - The first one that was a Latin adjective in its own right, not a negation.
- (in)trudes - From the Latin trudere (to push). In this case, the in- prefix doesn't mean the opposite, but rather "into" (therefore: extrudes).
- (de)ceptive - The Latin root capere (to take) took a slightly more roundabout route to "capable".
- (in)sipid - Related, somewhat, to the word "sapient", via the Latin root sapidus/sapere.
- (dis)traught - Distraught comes from the word "distract", perhaps modified like the past participles "caught" and "bought".
- (in)sist - From the Latin root sistere (take a stand). Like intrude, the prefix means in/on, although the reverse never made it to English. Related to assist.
- (non)chalantly - From the French non- and chaloir (have concern for)
- (un)gainly - From the Old Norse un- and gegn (convenient or direct). Related to "again" and "against".
- (in)digent - The prefix here isn't in-, but rather Latin indu and egere (need, want)
- (as)sertive - "Assert" is from the Latin asserere (to claim). (Aside: either this is out of place, or I'm misinterpreting which word the author was using. I see no way to interpret "as-" as a prefix)
- (in)choate - The last two are the most interesting. This word used to have a more straightforward and less judgemental meaning. From the Latin in- (meaning on) and, strangely, cohum (the strap fastened to an ox).
- (a)loof - The prefix "a-" is similar to the same prefix in anew or afoot, and the Middle English loof is from the Dutch loef (the weather side of a ship).
Final count: 11 negations, 5 prefixes with non-negation meanings, and 3 words not constructed with a prefix.