early 14c., "member of a militant 1st century Jewish sect which fiercely resisted the Romans in Palestine," from Late Latin zelotes, from Greek zelotes "one who is a zealous follower," from zeloun "to be zealous," from zelos "zeal" (see zeal). Extended sense of "a fanatical enthusiast" first recorded 1630s (earlier in this sense was zelator, mid-15c.).