Real Dictionary

filter in American English
a device for separating solid particles, impurities, etc. from a liquid or gas by passing it through a porous substance
intransitive verb: to pass or slip through slowly, as through an obstruction or a filter
noun: any substance, as cloth, paper, porous porcelain, or a layer of charcoal or sand, through which liquid or gas is passed to remove suspended impurities or to recover solids
transitive verb: to remove by the action of a filter

filter in Automotive Engineering
noun: A filter is a device through which air, fuel, or oil is passed to remove unwanted particles.

filter in Chemical Engineering
noun: A filter is a vessel or stage in which solids are removed from a liquid by passing it through something porous.