Grinder \Grind"er\, n. 1. One who, or that which, grinds. 2. One of the double teeth, used to grind or masticate the food; a molar. 3. (Zo["o]l.) The restless flycatcher ({Seisura inquieta}) of Australia; -- called also {restless thrush} and {volatile thrush}. It makes a noise like a scissors grinder, to which the name alludes.