Aerostat
/ˈerəstæt/
Definition 1 of 1
Pro Tip 1/3Specific Context
Used mostly in technical discussions about types of aircraft that stay aloft. 
The company designed a new aerostat for aerial surveillance.
Pro Tip 2/3Not Always Dirigible
An aerostat can be untethered like a balloon or tethered like a blimp. 
Observation aerostats are tethered to monitor areas for long durations.
Pro Tip 3/3Heavier-than-Air vs. Lighter-than-Air
Confused with airplanes, but aerostats are lighter-than-air vehicles. 
Unlike airplanes, aerostats don't rely on aerodynamic lift.