money-pit n.

mid-13c., monie, "funds, means, anything convertible into money;" c. 1300, "coinage, coin, metal currency," from Old French monoie "money, coin, currency; change" (Modern French monnaie), from Latin moneta "place for coining money, mint; coined money, money, coinage," from Moneta, a title or surname of the Roman goddess Juno, near whose temple on the Capitoline Hill money was coined (and in which perhaps the precious metal was stored); from monere "advise, warn, admonish" (on the model of stative verbs in -ere; see monitor (n.)), by tradition with the sense of "admonishing goddess," which is sensible, but the etymology is difficult. A doublet of mint (n.2)).

It had been justly stated by a British writer that the power to make a small piece of paper, not worth one cent, by the inscribing of a few names, to be worth a thousand dollars, was a power too high to be entrusted to the hands of mortal man. [John C. Calhoun, speech, U.S. Senate, Dec. 29, 1841] 

Extended by early 19c. to include paper recognized and accepted as a substitute for coin. The highwayman's threat your money or your life is attested by 1774. Phrase in the money (1902) originally referred to "one who finishes among the prize-winners" (in a horse race, etc.). The challenge to put (one's) money where (one's) mouth is is recorded by 1942 in African-American vernacular. Money-grub for "avaricious person, one who is sordidly intent on amassing money" is from 1768; money-grubber is by 1835. The image of money burning a hole in someone's pocket is attested from 1520s (brennyd out the botom of hys purs).

I am not interested in money but in the things of which money is the symbol. [Henry Ford]

Old English pytt (Kentish *pet), "natural or man-made depression in the ground, water hole, well; grave," from Proto-Germanic *putt- "pool, puddle" (source also of Old Frisian pet, Old Saxon putti, Old Norse pyttr, Middle Dutch putte, Dutch put, Old High German pfuzza, German Pfütze "pool, puddle"), an early borrowing from Latin puteus "well, pit, shaft."

The Latin word is perhaps from PIE root *pau- (2) "to cut, strike, stamp," but there are phonetic and sense objections.

Short u makes it impossible to directly derive puteus from paviō 'to strike'. It might be related to putāre 'to prune', but this is semantically less attractive, and the suffix -eus can then hardly be interpreted as indicating a material. Therefore, puteus may well be a loanword. [de Vaan]

Meaning "abode of evil spirits, hell" is attested from late 12c.  Meaning "very small depression or dent in the surface of an object" is from early 15c. The anatomical sense of "natural depression or hollow in some part of the body" is by late 13c,; the pit of the stomach (1650s) is so called from the slight depression there between the ribs; earlier words for it were breast-pit (late 14c.), heart-pit (c. 1300).

The meaning "part of a theater on the floor of the house, lower than the stage," is from 1640s; the sense of "that part of the floor of an exchange where business is carried on" is by 1903, American English. The pit dug under a large engine or other piece of machinery to allow workers to examine or repair it is attested by 1839; this later was extended in auto racing to "area at the side of a track where cars are serviced and repaired" (by 1912).