How does a word come to have two completely opposite meanings?

Words like cleave and egregious have meanings that are completely opposite to other meanings of the same word. How did such a bizarre, confusing state of affairs ever develop?

I mean, I just can't work out how one and the same word could come to mean two distinct things that are completely opposite! Is it the same root? What did the root mean and how did it come to be used to mean the opposite?

Solution 1:

If you start with wikipedia

An auto-antonym (sometimes spelled autantonym), or contranym (originally spelled contronym), is a word with a homograph (a word of the same spelling) that is also an antonym (a word with the opposite meaning). Variant names include antagonym, Janus word (after the Roman god), enantiodrome, and self-antonym. It is a word with multiple meanings, one of which is defined as the reverse of one of its other meanings.

it already puts you on the right path and mentions one of the word and one of the ways that can make such words

Some pairs of contronyms are true homographs, i.e., distinct words with different etymology which happen to have the same form. For instance cleave "separate" is from Old English clēofen, while cleave "adhere" is from Old English cleofian, which was pronounced differently. This is related to false friends, but false friends do not necessarily contradict.

In other words, for example literally, the two meanings developed from the overuse of the word as hyperbole.

Solution 2:

It's probably fair to say that the processes of language change aren't so well understood as other areas of linguistics. But, the following probably have an influence:

• certain words tend to get used alongside certain others as fixed colloquations
• as particular colloquations become common, the meaning of the individual words probably gets "spread" over the colloquation as a whole, and speakers don't necessarily process the individual words with their individual meanings, thus allowing the part of the overall meaning that's attributed to each individual word of the colloquation to "shift" slightly
• colloquations may be created and then shortened so that you accidentally end up with cases such as "terrific" (I suspect the process was something like "terrific" > "terrifically bad" > "terrifically good" > "terrific")
• in longer colloquations, you can replace one word with another of quite different meaning, and people may still interpret the overall colloqation has having a similar meaning because of this effect, e.g. you'll obesrve speakers using "It leaves much to be desired" vs "It leaves little to be desired" more or less interchangeably
• languages are "complex systems", and the frequency that words are used in different colloquations/usages can vary quite chaotically; meanwhile, if a word is used with a particular meaning only in a handful of colloquations, it is probably liable for those "minority" colloquations to be re-interpreted to fit the majority usage of a given word (this appears to have happned e.g. with "begs the question", which now tends to mean "requires the question to be asked" rather than "ignores the question", or "more haste less speed", where "speed" tends to have a more literal interpretation than its original meaning that was probably closer to "success")
• specifically with the case of words taking on their opposite meanings, a possible influence is that speakers appear to be quite bad at processing negatives. For example, speakers are liable to process pairs such as , or "No accident is too severe to ignore" vs "No accident is too trivial to ignore" as effectively meaning the same thing, even though "severe" and "trivial" have pretty much opposite meanings (this is similar to the "much to be desired" example, but specifically having a negative in the sentence appears to enhance the effect)
• there are probably cases where speakers deliberately pick the antonym of a word and use it with the same meaning ("you loser" > "you winner"), or deliberately choose a negative expression and actively use it with a positive meaning ("that's totally sick, man!")