1A small knob or lump; a nugget; = "nub". Also figurative. Also: a protuberance or swelling on the body. Compare "knob" 1a. Now somewhat rare (chiefly English regional in later use).
2The heart of a matter; the crux or central point of a discussion, argument, etc.
3 rare The innermost wrapping of a silkworm cocoon. Frequently in plural (often used to refer to waste silk in this form). Compare "nub".
Mid 16th century. Either (i) a variant of knob.