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pneumatocyst

American  
[noo-mat-uh-sist, nyoo-, noo-muh-tuh-, nyoo] / nʊˈmæt ə sɪst, nyʊ-, ˈnu mə tə-, ˈnyu /

noun

Biology.
  1. the cavity of a pneumatophore.

  2. pneumatophore.


Etymology

Origin of pneumatocyst

First recorded in 1855–60; pneumato- + -cyst