zealot

In the 1st century A.D., a fanatical sect arose in Judaea to oppose the Roman domination of Palestine. Known as the Zealots, they fought their most famous battle at the great fortress of Masada, where 1,000 defenders took their own lives just as the Romans were about to storm the fort. Over the years, zealot came to mean anyone who is passionately devoted to a cause. The adjective zealous may describe someone who's merely dedicated and energetic ("a zealous investigator", "zealous about combating inflation", etc.). But zealot (like its synonym fanatic) and zealotry (like its synonym fanaticism) are used disapprovingly—even while Jews everywhere still honor the memory of those who died at Masada.