Merriam-Webster's Collegiate® Dictionary, 11th Edition
GRIND
I. verb (ground; grinding)
Etymology: Middle English, from Old English grindan; akin to Latin frendere to crush, grind Date: before 12th century transitive verb to reduce to powder or small fragments by friction (as in a mill or with the teeth), to wear down, polish, or sharpen by friction ,
3. oppress , harass , to weaken or destroy gradually,
4. to press together with a rotating motion , to rub or press harshly , to operate or produce by turning a crank , intransitive verb to perform the operation of grinding, to become pulverized, polished, or sharpened by friction, to move with difficulty or friction especially so as to make a grating noise , drudge , to rotate the hips in an erotic manner, grindingly adverb
II. noun
Date: 13th century
1. an act of grinding, the sound of grinding,
2. dreary, monotonous, or difficult labor, study, or routine, one who works or studies excessively, the result of grinding, the act of rotating the hips in an erotic manner, see: work