Word Origin & History
O.E. cnotta "intertwining of ropes, cords, etc.," from P.Gmc. *knuttan- (cf. Low Ger. knütte, Du. knot, O.H.G. knoto, Ger. Knoten, perhaps also O.N. knutr "knot, knob"). Fig. sense of "difficult problem" was in O.E. (cf. Gordian knot). Symbolic of the bond of wedlock, 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. The nautical unit of measure (1630s) is from the practice of attaching knotted string to the log line. 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]
The verb meaning "to tie in a knot" is from 1547. Knot-hole is from 1726. Knothead "stupid person" is from 1940.