Etymology
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plumber (n.)

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.)). The meaning focused 19c. on "workman who installs pipes and fittings" as lead pipes for conveying water and gas became the principal concern of the trade.

In U.S. history, in the Nixon administration (1969-74), it was the name of a special unit for investigation of "leaks" of government secrets.

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plunger (n.)

1610s, "one who plunges," agent noun from plunge (v.). Used of various mechanisms (for example the dasher of a churn) by 1777; as "device used by a plumber to clear blocked pipes," by 1936.

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plumb (v.)

late 14c., plumben, "to sink" (like lead); mid-15c., "weight (a fishing line)," from plumb (n.). Meaning "take soundings with a plumb" is recorded from 1560s; the figurative sense of "to get to the bottom of" is from 1590s. The meaning "to work as a plumber" is by 1889. Related: Plumbed; plumbing.

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crap (v.)

"to defecate," 1846, from a cluster of older nouns, now dialectal or obsolete, applied to things cast off or discarded (such as "weeds growing among corn" (early 15c.), "residue from renderings" (late 15c.), underworld slang for "money" (18c.), and in Shropshire, "dregs of beer or ale"), all probably from Middle English crappe "grain that was trodden underfoot in a barn, chaff" (mid-15c.), from French crape "siftings," from Old French crappe, from Medieval Latin crappa, crapinum "chaff." Related: Crapped; crapping.

For connection of the idea of defecation with that of shedding or casting off from the body, compare shit (v.). Despite the etymological legend, the word is not from the name of Thomas Crapper (1837-1910) who was, however, a busy plumber and may have had some minor role in the development of modern toilets. The name Crapper is a northern form of Cropper (attested from 1221), an occupational surname, obviously, but the exact reference is unclear. Crap (v.) as a variant of crop (v.) was noted early 19c, as a peculiarity of speech in Scotland and what was then the U.S. Southwest (Arkansas, etc.).

Draw out yere sword, thou vile South'ron!
   Red wat wi' blude o' my kin!
That sword it crapped the bonniest flower
   E'er lifted its head to the sun!
[Allan Cunningham (1784-1842), "The Young Maxwell"]
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