Bouser comes from bouse (a variant of booze, 'to drink heavily') + -er. Bouse descends from Middle Dutch būsen ('to drink to excess'). The historical trail runs through būsen in Middle Dutch. Morphologically, bouser is transparent: it draws on bouse (a variant of booze, 'to drink heavily') + -er. Used as a noun, bouser now means "dialectal a heavy drinker or carouser; one who bouses", so the present definition can be read against the older forms and meanings. The same lexical family is also visible in related forms such as bouse and booze. The result is a borrowed or transmitted form whose modern spelling carries a compact record of its route into English.