1. Someone who is very enthusiastic, especially excessively so.
2. A fanatically committed person.
3. A zealot was a member of a Jewish movement of the first century A.D. that fought against Roman rule in Palestine as incompatible with strict monotheism.

A sect of Jews who originated with Judas the Gaulonite (Acts 5:37). They refused to pay tribute to the Romans, on the ground that this was a violation of the principle that God was the only king of Israel. They rebelled against the Romans, but were soon scattered, and became a lawless band of brigands or bandits. They were afterwards called Sicarii, because of their use of the sica, the Roman dagger.