Definition of stuff:

part of speech: verb

To fill very full; to crowd; to press; to cause to swell out by putting something in; to thrust into; to fill meat with seasoning; to obstruct, as one of the organs; to fill, as the skin of a dead animal for preserving its likeness; to feed gluttonously.

part of speech: noun

Any collection of substances; materials of which anything is made; the woven fabric of which clothes are made; something trifling or worthless.