"resinous knot of a pine tree, used as fuel," 1660s, from pine (n.1) + knot (n.).
Entries linking to pine-knot
pine n.
"coniferous tree, tree of the genus Pinus," Old English pin (in compounds), from Old French pin and directly from Latin pinus "pine, pine-tree, fir-tree," which is perhaps from a PIE *pi-nu-, from root *peie- "to be fat, swell" (see fat (adj.)).
If so, the tree's name would be a reference to its sap or pitch. Compare Sanskrit pituh "juice, sap, resin," pitudaruh "pine tree," Greek pitys "pine tree." Also see pitch (n.1). The native Old English word was furh (see fir). Pine-top "cheap illicit whiskey," is attested by 1858, Southern U.S. slang.
Most of us have wished vaguely & vainly at times that they knew a fir from a pine. As the Scotch fir is not a fir strictly speaking, but a pine, & as we shall continue to ignore this fact, it is plain that the matter concerns the botanist more than the man in the street. [Fowler]
knot n.
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).