Both Uses

geosynchronous
in
The Hunt for Red October
(Auto-generated)

The next wake-up signal, AAA—encrypted, of course—would alert them to go to periscope-antenna depth to get more detailed instructions from SSIX, the submarine satellite information exchange, a geosynchronous communications satellite used exclusively by submarines.†
Chpt 5. *

geosynchronous = orbiting Earth once per day
His neighbor at the next console was watching data from a geosynchronous weather satellite that monitored the Western Hemisphere.†
Chpt 16.

Definitions:

(1) (geosynchronous)
orbiting Earth once per day so the satellite comes back to the same place in the sky at the same time each day; or so it seems fixed in one spot above the equator

In a geosynchronous orbit, the satellite’s orbital period matches Earth’s rotation period (about 24 hours). If the orbit is also circular and directly above the equator, the satellite appears to stay above the same point on Earth all the time; that special case is called a geostationary orbit. People often use geosynchronous to refer to this geostationary case.
(2) (meaning too rare to warrant focus)