"stopper, faucet through which liquid can be drawn," Old English tæppa "tap, spigot," from Proto-Germanic *tappon (source also of Middle Dutch tappe, Dutch tap, Old High German zapfo, German Zapfe). Originally a tapering cylindrical peg for a cask, then a hollowed one to draw from it (compare sense evolution of spigot). Phrase on tap "ready for use, ready to be drawn and served" is recorded from late 15c. Tap-wrench, used in turning one, attested from 1815.
Old English wrencan "to twist," from Proto-Germanic *wrankjan (source also of Old High German renken, German renken "to twist, wrench," Old English wringan "to wring"), from PIE *wreng- "to turn" (source also of Sanskrit vrnakti "turns, twists," Lithuanian rengtis "to grow crooked, to writhe"), nasalized variant of *werg- "to turn" (source also of Latin vergere "to turn, tend toward"), from root *wer- (2) "to turn, bend." Related: Wrenched, wrenching.
Old English wrenc "a twisting, artifice, trick;" see wrench (v.). The meaning "tool with jaws at one end for turning or holding" is first recorded 1794.
"device to listen in secretly on telephone calls," 1923, from tap (v.2) in the "listen secretly" sense.
"to supply with a tap," late Old English tæppian, from source of tap (n.1); compare German zapfen "to tap." Meaning "to draw liquor with a tap" is from mid-15c. Extended sense "make use of" is first recorded 1570s. Meaning "listen in secretly" (1869), originally was with reference to telegraph wires. Tapped out "broke" is 1940s slang, perhaps from the notion of having tapped all one's acquaintances for loans already (compare British slang on the tap "begging, making requests for loans," 1932).
"light blow or stroke," mid-14c., from tap (v.1). Tap dancer first recorded 1927, from tap (n.) in the sense of "metal plate over the heel of a shoe" (1680s).
"strike lightly," c. 1200, from Old French taper "tap, rap, strike" (12c.), from a Gallo-Roman or Germanic source ultimately imitative of the sound of rapping. Meaning "to designate for some duty or for membership" is recorded from 1952, from notion of a tap on the shoulder. Related: Tapped; tapping.
also heeltap, 1680s, "one of the bits of leather that are stacked up to make a shoe heel" (see heel (n.1)); meaning "bit of liquor left in a glass or bottle" first recorded 1767; the exact connection is uncertain unless it be "the last or final part." Related: Heeltaps.
A jolly dog, is one who has no conversation in company, but "fill about, what's the toast, damn your heel-taps," and roars out an obscene ballad when he gets drunk. [The Batchelor, March 28, 1767]
old style of wrench with a jaw adjustable by a screw mechanism on the handle, 1841, from monkey (n.) + wrench (n.). Monkey was used in 19c. especially by sailors, as a modifier for various types of small equipment made for specific work (monkey-block, monkey-boat, monkey-spar, etc.), and the same notion probably is behind the name of the tool. The figurative sense of "something that obstructs operations" is from the notion of one getting jammed in the gears of machinery (compare English spanner in the works).
