Definition of "aerostat"

aerostat

noun
plural aerostats
1. An aircraft, such as a dirigible or balloon, that derives its lift from buoyancy rather than from wings or rotors.
  Quotations
  With its molten temperatures, sulphuric acid clouds, and crushing carbon dioxide atmosphere, Venus has only a handful of aerostat research outposts.
  2008, BioWare, Mass Effect (Science Fiction), Redwood City: Electronic Arts, PC, scene: Venus
2. A moored balloon flown in a semi-permanent manner, such as a border patrol monitoring balloon affixed at 18,000 feet (~6 km).