Quaternary
Part of speech: adjective
Definition: Of fourth rank or order. Of a mathematical expression containing e.g. x4.
Quartet
Part of speech: noun
Definition: A music composition in four parts, each performed by a single voice or instrument.The set of four musicians who perform a piece of music together in four parts.A group of four.
Example sentence: Industry, economy, honesty, and kindness form a quartet of virtues that will never be improved upon.