The origin of the word Jazz is one of the most sought-after word origins in modern American English. The word's intrinsic interest - the American Dialect Society named it the Word of the Twentieth Century - has resulted in considerable research, and its history is well-documented. As discussed in more detail below, jazz began as a West Coast slang term around 1912, the meaning of which varied but which did not refer to music or sex. Jazz came to mean jazz music in Chicago around 1915. Jazz was played in New Orleans prior to that time but was not called jazz.

The earliest known references to jazz are in the sports pages of various West Coast newspapers covering the Pacific Coast League, a baseball minor league. The earliest example, found by New York University librarian George A. Thompson, Jr. in 2003, is from the Los Angeles Times on April 2, 1912, referring to Portland Beavers pitcher Ben Henderson:

BEN'S JAZZ CURVE. "I got a new curve this year," softly murmured Henderson yesterday, "and I'm goin' to pitch one or two of them tomorrow. I call it the Jazz ball because it wobbles and you simply can't do anything with it." As prize fighters who invent new punches are always the first to get their's Ben will probably be lucky if some guy don't hit that new Jazzer ball a mile today. It is to be hoped that some unintelligent compositor does not spell that the Jag ball. That's what it must be at that if it wobbles.

Henderson's jazz ball apparently was not a success, as there are no known further references to it except for a brief mention in the Times the following day. While the lack of further attestations shows that Henderson is unlikely to have played a significant role in the popularization of jazz, his early use proves that the word was in existence by 1912.

A more lasting influence emerged in 1913, in a series of articles by E.T. "Scoop" Gleeson in the San Francisco Bulletin, found by researchers Peter Tamony (who carried out the pioneering research in this area) and Dick Holbrook, that likely were instrumental in bringing jazz to a broader public. These initial articles were written in Boyes Springs, California, where the San Francisco Seals baseball team was in training. In the earliest reference, on March 3, 1913, jazz was used in a negative sense, to indicate that disparaging information about ball player George Clifford McCarl had turned out to be inaccurate: "McCarl has been heralded all along the line as a 'busher,' but now it develops that this dope is very much to the 'jazz.'"

Three days later, on March 6, Gleeson used jazz extensively in a longer article, in which he explained the term's meaning, which had now turned from negative to positive connotations:

Everybody has come back to the old town full of the old "jazz" and they promise to knock the fans off their feet with their playing. What is the "jazz"? Why, it's a little of that "old life," the "gin-i-ker," the "pep," otherwise known as the enthusiasalum. A grain of "jazz" and you feel like going out and eating your way through Twin Peaks. It's that spirit which makes ordinary ball players step around like Lajoies and Cobbs.

The article uses jazz several more times and says that the San Francisco Seals' "members have trained on ragtime and 'jazz' and manager Del Howard says there's no stopping them." The context of the article as a whole shows that a musical meaning of jazz is not intended; rather, ragtime and "jazz" were both used as markers of ebullient spirit.

Gleeson used jazz in a number of articles in March and April 1913, and other journalists began to use the term as well. The Bulletin on April 5, 1913, published an article by Ernest J. Hopkins entitled "In Praise of 'Jazz,' a Futurist Word Which Has Just Joined the Language." The article, which used the spellings jaz and jazz interchangeably, discussed the term at length and included a highly positive definition:

"JAZZ" (WE CHANGE the spelling each time so as not to offend either faction) can be defined, but it cannot be synonymized. If there were another word that exactly expressed the meaning of "jaz," "jazz" would never have been born. A new word, like a new muscle, only comes into being when it has long been needed. This remarkable and satisfactory-sounding word, however, means something like life, vigor, energy, effervescence of spirit, joy, pep, magnetism, verve, virility ebulliency, courage, happiness--oh, what's the use?--JAZZ.

Jazz, in the sense of pep and enthusiasm, continued in use in California for several years before being submerged by the jazz music meaning. Amateur etymologist Barry Popik has located a number of examples from the Berkeley Daily Californian and the Daily Palo Alto, showing that jazz in this sense was collegiate slang at the University of California, Berkeley in the period 1915 to 1917 and at Stanford University in the period 1916 to 1918. President Benjamin Ide Wheeler at Berkeley apparently used jazz with such frequency that many supposed he originated the term, although the Daily Californian stated on February 18, 1916, that he denied this.

As with many words that began in slang, there is no definitive etymology for jazz. However, the similarity in meaning of the earliest jazz citations to jasm, a now-obsolete slang term meaning spirit, energy, vigor and dated to 1860 in the Historical Dictionary of American Slang, suggests that jasm should be considered the leading candidate for the source of jazz. A link between the two words is particularly supported by the Daily Californian's February 18, 1916, article, which used the spelling jaz-m, although the context and other articles in the Daily Californian from this period show that jazz was intended. Jasm is thought to derive from or be a variant of slang jism or gism, which the Historical Dictionary of American Slang dates to 1842 and defines as "spirit; energy; spunk." Jism also means semen or sperm, the meaning that predominates today, causing jism to be considered a taboo word. In the 19th and early 20th centuries, however, jism could still be used in polite contexts. Jism, or its variant jizz (which, however, is not attested in the Historical Dictionary of American Slang until 1941), has also been suggested as a direct source for jazz. A direct derivation from jism is phonologically unlikely; jasm itself would be, according to this assumption, the intermediary form.

Other proposed origins include French jaser, meaning to chatter or chat, and French chasser, meaning to chase or hunt. Daniel Cassidy, a film-maker, musician, and writer, has argued for a derivation from Irish teas, which is pronounced /t?�s/ ("chass") and means "heat". Although they cannot be ruled out absolutely, such derivations lack empirical supporting evidence and must be considered speculative.

Scoop Gleeson, who first popularized the word, wrote in an article in the Call-Bulletin on September 3, 1938, that he learned the word from sports editor William "Spike" Slattery when the two were at Boyes Springs. Gleeson said that Slattery had picked up the expression in a craps game. "Whenever one of the players rolled the dice he would shout 'Come on, the old jazz.'" Assuming the accuracy of this noncontemporaneous recollection, the craps use of jazz appears to be a nonce-use and does not provide much information about the word's origin.

The association of jazz with sex is early and extensive. The Historical Dictionary of American Slang (1997) cites explicit sexual meanings from 1918 and says that this was probably the original sense. However, it now seems difficult to reconcile a prior, widely recognized sexual meaning of jazz with the known word history described above. Professor Gerald Cohen of Missouri University of Science and Technology, who has done a great deal of work on the word's history, in 2001 offered a $100 reward for any provable musical or sexual use of jazz from before 1913, an offer that still stands.

Vet Boswell of the Boswell Sisters said she remembered when "jazz" was not a word fit to be uttered in polite company. Ray Lopez of Tom Brown's 1915 band recalled he and his fellow musicians assumed that the word "jass" or "jazz" was too improper to be printed in newspapers so they looked in a dictionary for similar words like "jade"; rediscovered newspaper advertisements from the era for Brown's "Jad Band" or "Jab Band" are suggestive of confirmation of this account