subbase
nounUK /ˈsʌbˌbeɪs/
US /ˈsʌbˌbeɪs/
A strong layer under a road or floor that holds everything up.
Workers spread gravel as a subbase before pouring the concrete.
RELATED WORDS
OTHER MEANINGS
2. A base that is itself placed on another base, especially in mathematics.
The topology was defined using a subbase of open sets.
3. A secondary or lower base in a machine or structure.
The motor sits on a steel subbase bolted to the floor.
4. In baseball, a base other than home plate.
The runner slid safely into the subbase.