Roust a 17th-century variant of rouse, of uncertain ultimate origin; the additional -t may be by analogy with other verbs. Morphologically, roust is best read as uncertain formation, yielding an English verb shaped by both form history and later usage. In current English it functions as a verb, with the sense "to rouse or stir up, often roughly; to drive out". English derivatives include rousted, rousting, and roustabout; related forms include rouse. The result is an English verb whose etymology preserves the older forms while supporting the word's specialized modern meaning.