- any large, stinging paper wasp of the family Vespidae, as Vespa crabro(giant hornet ), introduced into the U.S. from Europe, or Vespula maculata(bald-faced hornet, or white-faced hornet ), of North America.
- any of various large social wasps of the family Vespidae, esp Vespa crabro of Europe, that can inflict a severe sting
- a strongly unfavourable reaction (often in the phrase stir up a hornet's nest)
