mid-15c., rousen, intransitive, probably from Anglo-French or Old French reuser, ruser; Middle English Compendium compares 16c. French rousee "abrupt movement." Sometimes also said to be from Latin recusare "refuse, decline," with loss of the medial -c-. Originally in English a technical term in hawking, "to shaking the feathers of the body," but like many medieval hawking and hunting terms it is of obscure origin.
The sense of "cause game to rise from cover or lair" is from 1520s. The word became general from 16c. in the figurative, transitive, meaning "stir up, cause to start up by noise or clamor, provoke to activity; waken from torpor or inaction" (1580s); that of "to awaken, cause to start from slumber or repose" is recorded by 1590s. Related: Roused; rousing.