noun

1. a knot; knob; swelling
2. a point of concentration; central point
3. Anat. a knotty, localized swelling; protuberance
4. Astron. either of the two diametrically opposite points at which the orbit of a celestial body intersects a reference plane, as the ecliptic
5. Bot. that part, or joint, of a stem from which a leaf starts to grow
6. Geom. the point where a continuous curve crosses or meets itself
7. Physics the point, line, or surface of a vibrating object, as a string, virtually free of vibration

Etymology: L nodus, a knot: see net