(cycling) The toughest category of climbs, tougher than category 1. One of six categories of climbs, HC, 1, 2, 3, 4, and not classified; not classified being the easiest.

(organic chemistry) Any iodo- derivative of amphetamine, but especially para-iodoamphetamine that is used as a selective serotonin releasing agent

(obsolete) A physician who treats the insane.

present participle of grade