Cantharus may refer to:
- Cantharus (Christianity), a fountain used by Christians for making ablutions
- Kantharos (also spelled cantharus), a Greek drinking cup
- Kantharos (also spelled Cantharus), an ancient Athenian comic poet
- Kantharos (also spelled Cantharus), a harbour in ancient Athens
- Sea snails in the family Pisaniidae, including:
- Cantharus, a genus of sea snails
- Common cantharus (Gemophos auritulus)
- Measle-mouth cantharus (Gemophos sanguinolentus)
- Ringed cantharus (Gemophos ringens)
- Tinted or painted cantharus (Gemophos tinctus)
- Ribbed cantharus (Hesperisternia multangula)