a tight cluster of people or things
"a small knot of women listened to his sermon"
"the bird had a knot of feathers forming a crest"
any of various fastenings formed by looping and tying a rope (or cord) upon itself or to another rope or to another object
"The sailor tightened the knot at the end of the rope before securing it to the railing."
a hard cross-grained round piece of wood in a board where a branch emerged
"the saw buckled when it hit a knot"
(of ships and wind) a unit of speed equal to one nautical mile per hour or about 1.15 statute miles per hour
"The sailor reported that their ship was traveling at twenty knots through the heavy storm."
a sandpiper that breeds in the Arctic and winters in the southern hemisphere
"The knot migrated south from its Arctic breeding grounds to spend the winter in New Zealand."
A looping of a piece of string or of any other long, flexible material that cannot be untangled without passing one or both ends of the material through its loops.
"During the migration season, we spotted several knots resting on the tidal flats."
One of a variety of shore birds; the red-breasted sandpiper (variously Calidris canutus or Tringa canutus).
In plain English: A knot is a tight loop tied around something to hold it fast, often used on rope or string.
"She tied her hair up in a messy knot before leaving for school."
Usage: Use "knot" as a noun to describe a loop in rope where the ends cannot be untangled without passing through each other, and use it as a verb when you are tying such a loop. Avoid confusing this term for unrelated concepts like birds or mathematical constants unless specifically referring to those distinct definitions.
To form into a knot; to tie with a knot or knots.
"The sailor tightened the rope and carefully knotted it around the pylon before climbing aboard."
In plain English: To knot something is to tie it into a tight, tangled loop that doesn't come apart easily.
"She tied a knot in her scarf to keep it from flying away in the wind."
The word knot comes from Old English cnotta, which likely traces back to a Proto-Indo-European root meaning "to bind." It entered modern usage as the familiar term for a tied loop or a dense cluster.