Blowhard, Esq. writes:

We’ve talked about polysemy several times, the phenomenon of one word having several meanings, some of which eventually come to overlap. An example is the word uncouth, the history of which we can chart with information from the OED. The word couth comes from a Germanic root meaning “known.”

Dates of Usage: Meaning of Uncouth

Old English–1650: unknown
Old English, now obsolete: unfamiliar or strange
1380–present: strange or unpleasant
1513–present: uncomely, awkward, clumsy
1542–present: rough, rugged
1694–present: uncultured

Note how the meaning of uncouth moves from a particular condition to a description grounded in that condition. Something that is unknown becomes alien, strange, weird, rugged, rough, and finally, uncultured. Couth has since taken on an imagined status, as in the phrase “He’s got no couth.” The usage here is completely ahistorical. Future lexicographers may record couth as a word emerging in the late 20th century to mean “propriety, ability, culture, knowledge, or skill.”

Excerpted from Seth Lerer’s History of the English Language, 2nd Edition course guidebook