1. In zoology, a gas-filled sac serving as a float in some colonial marine hydrozoan: On the internet, Lois read about the Portuguese man-of-war having a pneumatophore, to keep it buoyant.
2. In botany, a specialized structure or aerial root in certain plants serving as a respiratory organ: The mangroves growing in swamps and marshes possess pneumatophores in order to flourish.
3. A device that has an oxygen-filled bag and a tube that can be attached to an individuals's body: A pneumatophore is worn by a person when doing rescue work in mines.