ˈsəb+ˌ- noun
Etymology: sub- + station
: a station subordinate or subsidiary to another station: as
a. : a station which is subsidiary to a central station and at which high-tension electricity from the central station is transformed to electricity lower in potential and converted if desired to continuous current or to alternating current of a different frequency
b. : a small post-office station (as a contract station in a drug store or a station set up at a convention for handling philatelic mail)
c. : a subordinate station that rebroadcasts messages from a primary station of a communication system