Origin and history of knot-hole

Middle English hol, hole, "a perforation, an opening, a pore;" from Old English hol (adj.) "hollow, concave;" as a noun, "hollow place; cave; orifice; perforation," from Proto-Germanic *hulan, which is reconstructed (Watkins) to be from PIE root *kel- (1) "to cover, conceal, save." Perhaps also partly from Scandinavian.

As an adjective, except in dialects it was displaced by hollow, which in Old English only was a noun meaning "excavated habitation of certain wild animals."

Germanic cognates include Old Saxon, Old Frisian, Old High German hol, Middle Dutch hool, Old Norse holr, Danish hul, hule, German hohl "hollow," Gothic us-hulon "to hollow out." For the English vowel change, see extensive note in OED (1989).

In reference to hollows or cavities of the body by c. 1300. As a small cavity into which the ball is to be sunk in certain games, by 1580s. As a contemptuous word for "small, dingy lodging or abode" hole is attested from 1610s; as the worst cell in a prison, by 1530s, originally of London's "Counter" prison for debtors and petty offenders.

 The meaning "a fix, scrape, mess" is from 1760. In lower New England geography, "shallow cove, indentation of the coast" (1630s, as in Wood's Hole). Obscene slang use for "vulva" is implied from mid-14c.

The golfing hole-in-one is attested by 1914; as a verbal phrase (hole it in one) by 1913 (see hole (v.)). To need (something) like a hole in the head, applied to something useless or detrimental, is attested by 1944 in entertainment publications, probably a translation of a Yiddish expression such as ich darf es vi a loch in kop.

Old English cnotta "intertwining of ropes, cords, etc.," from Proto-Germanic *knuttan- (source also of Low German knütte, Old Frisian knotta "knot," Dutch knot, Old High German knoto, German Knoten, perhaps also Old Norse knutr "knot, knob"). For pronunciation, see kn-.

Figurative sense of "difficult problem, a perplexity" was in Old English (compare Gordian knot). Symbolic of the bond of wedlock from early 13c. As an ornament of dress, first attested c. 1400. Meaning "thickened part or protuberance on tissue of a plant" is from late 14c. As "small group or cluster of persons" late 14c.

The nautical unit of measure of speed (1630s) is from the practice of attaching knotted string to the log line at equal distances (see log (n.2)). The ship's speed can be measured by the number of knots that play out while the sand glass is running.

The distance between the knots on the log-line should contain 1/120 of a mile, supposing the glass to run exactly half a minute. [Jorge Juan and Antonio de Ulloa, "A Voyage to South America" 1760]

Hence the word knot came also to be used as the equivalent of a nautical mile (in pre-World War II use in U.S. and Britain, about 6,080 feet). A speed of 10 knots will cover ten nautical miles in an hour (equivalent to a land speed of about 11.5 mph).