pneu·ma·to·phore \ˈn(y)üməd.əˌfō(ə)r, n(y)üˈmad.əˌ-\noun (-s) Etymology: International Scientific Vocabulary pneumat- + -phore 1.: a muscular gas-containing sac that serves as a float on a siphonophore colony (as of members of the genus Physalia) 2.: a submerged or exposed root often functioning as a respiratory organ of a swamp or marsh plant