Old English cnotta "intertwining of ropes, cords, etc.," from Proto-Germanic *knuttan- (cf. Low German knütte, Old Frisian knotta "knot," Dutch knot, Old High German knoto, German Knoten, perhaps also Old Norse knutr "knot, knob"). Figurative sense of "difficult problem" was in Old English (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.