Pronunciation: (sub'bās"),[key] —n. 1. Archit.the lowest part of a base, as of a column, that consists of two or more horizontal members.
2. Math.a collection of subsets of a topological space having the property that every open set of a given topology can be written as the union of intersections of finite numbers of sets in the collection. Cf. base1 (def. 13b).