…a porous device for removing impurities or solid particles from a liquid or gas passed through it…
…a device for filtering particles of dust, soot, etc., from the air passing through it, especially one protecting the air inlet of an internal combustion engine…
…a tank or pond containing a layer of sand or gravel, used for filtering large quantities of liquid…
…a filter attached to a cigarette for removing some components from the inhaled smoke…
…a filter used in water purification and consisting of layers of sand arranged with coarseness of texture increasing downward…
…a piece of porous paper for filtering liquids, used especially in chemical processes and coffee-making…
…a device consisting of a series of cloth filters fixed to frames, used for the large-scale filtration of liquid under pressure…
…(of an aquatic animal) feeding by filtering out plankton or nutrients suspended in the water…
…a very slightly pink filter that reduces haze and excessive blueness of the sky in photographs by absorbing ultraviolet light…
…a photographic or optical filter that polarizes the light passing through it, used chiefly for reducing reflections and improving contrast. Two polarizing filters are often used together, such that rotation of one of them results in a neutral density filter of variable density…
…a photographic or optical filter that absorbs light of all wavelengths to the same extent, causing overall dimming but no change in color…
