- Physical Chemistry. a filter for purifying sols, having a membrane with pores sufficiently small to prevent the passage of the suspended particles.
- Mathematics. a filter in a topological space, having the property that no other filter exists in the space having among its subsets all the subsets in the given filter.
verb (used with object)
- Physical Chemistry. to purify by means of an ultrafilter.
- a filter with small pores used to separate very small particles from a suspension or colloidal solution