grind

To rotate the hips erotically 

To break down a hard substance to a finer size or degree

To work excessively 

To never attend parties

Monotonous, difficult labor

To become pulverized or sharp through friction

To reduce to powder, or small fragments

To wear down

To create constant friction on hard materials 

To rub roughly

To create friction with the teeth

To cause pressure on subjects, as pressure caused by tyrants on their subjects

To weaken, destroy gradually

To press down with a rotating motion

To granulate coffee seeds