Source : Webster's Revised Unabridged Dictionary (1913)

Aerostat \A"["e]r*o*stat\, n. [F. a['e]rostat, fr. Gr. ? air + ?
   placed. See {Statics}.]
   1. A balloon.

   2. A balloonist; an a["e]ronaut.

Aerostat \A"["e]r*o*stat\, n. (A["e]ronautics)
   A passive balloon; a balloon without motive power.