Old English latin "in Latin," from Latin Latinus "Latin, Roman, in Latin," literally "belonging to Latium," the region of Italy around Rome, a name of uncertain origin. Possibly from PIE root *stela- "to spread, extend," with a sense of "flat country" (as opposed to the mountainous district of the Sabines), or from a prehistoric non-IE language. Old folk etymology connected it with Latin latere "to lie hidden," and a fable of Saturn.
The Latin word also is the source of Spanish and Italian ladino, Dutch latijn, German latein, Irish Gaelic laidionn (n.), Polish lacina, Russian latuinŭ. The more common form in Old English was læden (see Latin (n.)).
In reference to the Roman Catholic Church, 1550s. Used as a designation for "people whose languages descend from Latin" (1856), hence Latin America (1862). The Latin Quarter (French Quartier latin) of Paris, on the south (left) bank of the Seine, was the site of university buildings in the Middle Ages, hence it was the place where Latin was spoken. The surname Latimer means "interpreter," literally "a speaker of Latin."
In Old French the word was used very broadly, "speech, language:" "What Latin was to the learned, that their tongue was to laymen; hence latino was used for any dialect, even Arabic and the language of birds ...." [Donkin, "Etymological Dictionary of the Romance Languages," 1864].
Roughly speaking, Old Latin is the Latin before the classical period including early authors and inscriptions. Classical Latin flourished from about 75 B.C.E. to about 200 C.E., the Latin of Lucretius, Catullus, Caesar, Cicero, Virgil, Horace, Ovid, Livy, Seneca, etc.; it is the standard Latin of the grammars and dictionaries. Late Latin followed the classical period to about 600 and includes the early church fathers. Medieval Latin was the Latin of the Middle Ages, from about 600 to 1500. Modern Latin is Latin as written from about 1500 on, largely by scientific writers in description and classification. Vulgar Latin was the speech of the Roman home and marketplace, going on concurrently under Classical and Late Latin.
childish deformed language (there are many different versions), by 1889 (hog Latin in same sense is attested by 1807).
The animals play quite an important part in the naming [of children's languages], as the hog, dog, fly, goose, pigeon, pig, all give names, with Mr. Hog leading. Among the names the Latins take the lead, and Hog Latin leads the list, being accredited as naming nearly as many languages as all the other names combined. Besides Hog Latin, there is Dog Latin, Pig Latin, Goose Latin, and Bum Latin. Then there is Greekish and Peddlers' French and Pigeon English. ... Very few can give any reason for the naming of the languages. In fact, no one can fully say where the great majority of names came from, for in most cases in the naming the following pretty well expresses the difficulty: "It was born before I was. I can't tell how young I was when I first heard of it." ["The Secret Language of Children," in The North Western Monthly, October 1897]
For the language itself, compare loucherbem, a 20c. French slang similar to pig Latin, which takes its name from the form of the word boucher in that language (which is said to have originated among the Paris butchers).