The origin of the word jazz is one of the most sought-after etymologies in modern American English. Interest in the word – named the Word of the Twentieth Century by the American Dialect Society – has resulted in considerable research and the linguistic history is well documented. "Jazz" originated in slang around 1912 on the West Coast. The meaning varied, but the word did not initially refer to music. "Jazz" came to mean jazz music in Chicago around 1915.

The similarity of "jazz" to "jasm", an obsolete slang term meaning spirit, energy, and vigor, and dated to 1860 in the Random House Historical Dictionary of American Slang (1979), suggests that "jasm" should be considered the leading candidate for the source of "jazz".

The word "jasm" appeared in Josiah Gilbert Holland’s second novel, Miss Gilbert's Career (1860), and meant “lively," and was used to describe the "inexpressible personal force of the Yankee".

A link between the two words is supported by a February 18, 1916 article in the Daily Californian which used the spelling "jaz-m", although the context and other articles in the same newspaper from this period show that "jazz" was intended.

"Jasm" derives from or is a variant of the slang term "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, making "jism" a taboo word. Consistent with that etymology, the jazz composer Eubie Blake (1887-1983), when interviewed by a woman for Yale's Oral History of American Music project, refused to use the word "jazz" because he thought it was uncouth. Deepening the nexus among these words is the fact that "spunk" is also a slang term for semen and that "spunk"—like jism/jasm—also means spirit, energy, or courage (for example: "She showed a lot of spunk"). In the 19th and early 20th centuries, however, "jism" was still used in polite contexts. "Jism" or its variant "jizz" (which 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.

Compare the analogous relationship between the slang terms "spasm" 'a sudden burst of energy', as in spasm band, and "spaz(z)". Herbert Asbury names the "Razzy Dazzy Spasm Band", which appeared about 1895, as the first jazz band; he relates that a band of professional musicians who imitated their style and originally appeared, about 1900, under the same name, was, after the original Spasm Band turned up, billed as "Razzy Dazzy Jazzy Band".

One source draws from the 1936 book The French Quarter by Herbert Asbury for the claim that there was a band in New Orleans in 1895 named the "Razzy Dazzy Spasm Band". This source also claims a connection to the French verb jaser, meaning to chatter, and that "to jass" was heard in New Orleans to mean 'to excite' or 'to pep up'.

Baseball references were used by E.T. "Scoop" Gleeson in the San Francisco Bulletin. Dick Holbrook and Peter Tamony found articles written in Boyes Springs, California, where the San Francisco Seals baseball team was in training. In an article from March 3, 1913, "jazz" is synonymous with nonsense. George Clifford McCarl had been called a "busher", as in "bush league", meaning minor league or second rate. But Gleeson writes, on the contrary, "this dope is very much to the 'jazz'." Other uses occurred in "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 enthusiasm". The article says that "members have trained on ragtime and 'jazz' and manager Del Howard says there's no stopping them." The context of the article shows that a musical meaning of "jazz" is not intended; rather, ragtime and "jazz" were both used as markers of ebullient spirit.