nematocyst

/nɪˈmætəˌsɪst/
noun
  1. A tiny, stinging structure found in the cells of jellyfish, sea anemones, and other cnidarians, used to capture prey or defend against threats.
    • Each nematocyst contains a coiled, harpoon-like thread that injects toxin.
    • When a jellyfish tentacle touches your skin, thousands of nematocysts fire venom into it.
    • Scientists study nematocysts to understand how jellyfish sting and how to treat stings.