masc. proper name, Middle English Jon, Jan (mid-12c.), from Old French Jan, Jean, Jehan (Modern French Jean), from Medieval Latin Johannes, an alteration of Late Latin Joannes, from Greek Ioannes, from Hebrew Yohanan (longer form y'hohanan), said to mean literally "Jehovah has favored" or "Jah is gracious," from hanan "he was gracious."
Greek conformed the Hebrew ending to its own customs. The -h- in English was inserted in imitation of the Medieval Latin form. Old English had the Biblical name as Iohannes. As the name of John the Baptist and John the Evangelist, it was one of the most frequent Christian given names, and in England by early 14c. it rivaled William in popularity and was used generically (in Middle English especially of priests) and as an appellative (as in John Barleycorn, John Bull, John Q. Public). Somehow it also became the characteristic name of a Chinaman (1818).
The Latin name also is the source of French Jean, Spanish Juan, Italian Giovanni, Portuguese João, also Dutch Jan, Hans, German Johann, Russian Ivan. Welsh form was Ieuan, Efan (see Evan), but Ioan was adopted for the Welsh Authorized Version of the Bible, hence frequency of Jones as a Welsh surname.
"toilet," 1932, probably from jakes, used for "toilet" since 15c. Meaning "prostitute's customer" is from 1911, probably from the common, and thus anonymous, name by which they identified themselves. Meaning "policeman" is by 1901, from shortening of johndarm (1823), a jocular Englishing of gendarme.
"John Darm! who's he?" "What, don't you know!
In Paris he is all the go;
Like money here,—he's every thing;
A demigod—at least a king!
You cannot fight, you cannot drink,
Nor have a spree, nor hardly think,
For fear you should create a charm,
To conjure up the fiend John Darm!
["John Darm," in "Varieties in Verse," John Ogden, London, 1823]
masc. proper name, a familiar shortening of German and Dutch Johannes (see John). Used figuratively for "a German" or "a Dutchman" from 1560s.
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.