Meaning of heavier-than-air

heav•i•er-than-air

Pronunciation: (hev'ē-ur-un-âr'), [key]
— adj.
  1. (of an aircraft) weighing more than the air that it displaces, hence having to obtain lift by aerodynamic means.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.
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