Boiler comes from boil + -er (agent/instrument suffix). Boil derives from Middle English boilen, from Old French boillir, from Latin bullīre ('to bubble, boil'), from bulla ('bubble'). The historical trail runs through bullīre in Latin and bulla in Latin. Morphologically, boiler is transparent: it draws on boil + -er (agent/instrument suffix). Used as a noun, boiler now means "a vessel or apparatus for heating water or generating steam", so the present definition can be read against the older forms and meanings. The same lexical family is also visible in derived forms such as boilerplate, boilermaker, and boilerroom and related forms such as boil, boiling, and boiled. The result is a borrowed or transmitted form whose modern spelling carries a compact record of its route into English.