aer·o·stat 
(ârō-stăt′)
(ârō-stăt′)n.
An aircraft, especially a balloon or dirigible, deriving its lift from the buoyancy of surrounding air rather than from aerodynamic motion.
[French aérostat : Greek āero-, aero-; see AERO- + Greek statos, standing; see STATO-.]
aer′o·static, aer′o·stati·cal adj.