1. The hub of a wheel. See Hub.
2. The flat projection or iron shelf at the side of a fire grate, where things are put to be kept warm.
3. (Science: mechanics) a threaded and fluted hardened steel cutter, resembling a tap, used in a lathe for forming the teeth of screw chasers, worm wheels, etc.
Origin: Prob. Akin to hump. Cf. Hub.