mythical river of Hades (whose water when drunk caused forgetfulness of the past), in Homer, a place of oblivion in the lower world; from Greek lēthē, literally "forgetfulness, oblivion," from PIE root *ladh- "be hidden" (see latent). Related to lēthargos "forgetful" and cognate with Latin latere "to be hidden." Also the name of a personification of oblivion, a daughter of Eris. Related: Lethean.
colloquial for "signature," 1903 (sometimes, through some unexplainable error, John Henry), from the Boston merchant and rebel (1736-1793), signer of the U.S. Declaration of Independence. The extended sense is from his signing that dangerous document first or most flamboyantly.
John Hancock, president of Congress, was the first to sign the Declaration of Independence, writing his name in large, plain letters, and saying: "There; John Bull can read my name without spectacles. Now let him double the price on my head, for this is my defiance." [Hélène Adeline Guerber, "The Story of the Thirteen Colonies," New York, 1898]
The family name is attested from 1276 in Yorkshire, a diminutive (see cock (n.1)) of Hann, a very common given name in 13c. Yorkshire as a pet form of Henry or John.
mid-14c. (implied in Tartary, "the land of the Tartars"), from Medieval Latin Tartarus, from Persian Tatar, first used 13c. in reference to the hordes of Ghengis Khan (1202-1227), said to be ultimately from Tata, a name of the Mongols for themselves. Form in European languages probably influenced by Latin Tartarus "hell" (e.g. letter of St. Louis of France, 1270: "In the present danger of the Tartars either we shall push them back into the Tartarus whence they are come, or they will bring us all into heaven").
The historical word for what now are called in ethnological works Tatars. A Turkic people, their native region was east of the Caspian Sea. Ghengis' horde was a mix of Tatars, Mongols, Turks, etc. Used figuratively for "savage, rough, irascible person" (1660s). To catch a Tartar "get hold of what cannot be controlled" is recorded from 1660s; original sense not preserved, but probably from some military story similar to the old battlefield joke:
Irish soldier (shouting from within the brush): I've captured one of the enemy.
Captain: Excellent! Bring him here.
Soldier: He won't come.
Captain: Well, then, you come here.
Soldier: I would, but he won't let me.
Among the adjectival forms that have been used are Tartarian (16c.), Tartarous (Ben Jonson), Tartarean (17c.); Byron's Tartarly (1821) is a nonce-word (but a good one). Tartar sauce is attested by 1855, from French sauce tartare.