ˈsəb+ˌ- noun
Etymology: sub- + base
1.
a. : another base, foundation, or other underlying support placed below that which ordinarily forms the base
b. : the lowermost part of a base ; specifically : the lowest member of an architectural base (as when divided horizontally) or of a baseboard or pedestal
c. : material placed under or designed for use under a base
2. : an alternate or satellite air base subordinate to a main air base commander either directly or administratively or logistically