1896, "red or white dry California wine," origin uncertain; used earlier as the name of the grape from which it was made (1880). The wine itself is said to have been known in U.S. since 1829. Some wine experts suggest a corruption of the Austrian grape name Zierfandler, though these grapes are not related to those of zinfandel. See this article:
The similarity in the names Zinfandel and Zierfandler arouses some speculation. Modern vine identification systems did not yet exist in 1829, so it is conceivable that the cuttings George Gibbs imported to the USA had never been correctly identified in Austria.