noun

• (mathematics) A non-self-intersecting closed curve in (e.g., three-dimensional) space that is an abstraction of a knot (in sense 1 above).
  "A knot can be defined as a non-self-intersecting broken line whose endpoints coincide: when such a knot is constrained to lie in a plane, then it is simply a polygon."
• (engineering) A node (point at which the lines of a funicular machine meet from different angular directions)
• (aviation, nautical) A unit of speed, equal to one nautical mile per hour.
  "Cedric claimed his old yacht could make 12 knots."
• (aviation) A unit of indicated airspeed, calibrated airspeed, or equivalent airspeed, which varies in its relation to the unit of speed so as to compensate for the effects of different ambient atmospheric conditions on aircraft performance.
  "In the early stages of reentry, due to the extremely-rarefied air at these altitudes, the space shuttle flew at only one to a few knots equivalent airspeed, even when its actual speed was many thousands of knots."

verb

• (transitive) To form into a knot; to tie with a knot or knots.
  "We knotted the ends of the rope to keep it from unravelling."
• (transitive) To form wrinkles in the forehead, as a sign of concentration, concern, surprise, etc.
  "She knotted her brow in concentration while attempting to unravel the tangled strands."
• (transitive, obsolete, rare) To entangle or perplex; to puzzle.
• (intransitive) To form knots.