late 14c. (from c.1100 as a surname), "a worker in any sort of lead" (roofs, gutters, pipes), from Old French plomier "lead-smelter" (Modern French plombier) and directly from Latin plumbarius "worker in lead," noun use of adjective meaning "pertaining to lead," from plumbum "lead" (see plumb (n.)). Meaning focused 19c. on "workman who installs pipes and fittings" as lead water pipes became the principal concern of the trade. In U.S. Nixon administration (1969-74), the name of a special unit for investigation of "leaks" of government secrets.
Those who attempted to bring plumbing indoors faced technical as well as attitudinal challenges. Decisions on how wastewater was removed required as much concern as those made to ensure an adequate water supply. But equally vexing was the prevailing miasma theory of disease, which held that illnesses stemmed from "bad air" that was readily identifiable by its offensive odor. This led to a distrust of early indoor plumbing that tended to leak and a deadly fear of the sewer gas that accompanied the leaks. It is no wonder then that many individuals maintained a strong belief that elimination was best taken care of out of doors.