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Definition of filter
a porous device for removing impurities or solid particles from a liquid or gas passed through it:an oil filter short for filter tip. [as modifier]:a cheap filter cigarette a screen, plate, or layer of a substance that absorbs light or other radiation or selectively absorbs some of its components:filters can be used in photography to reduce haze a device for suppressing electrical or sound waves of frequencies not required. Computing a piece of software that processes text, for example to remove unwanted spaces or to format it for use in another application. British an arrangement whereby vehicles may turn left (or right) while other traffic waiting to go straight ahead or turn right (or left) is stopped by a red light: [as modifier]:a filter lane
verb [with object]
1pass (a liquid, gas, light, or sound) through a device to remove unwanted material:the patient is hooked up to a dialysis machine twice a week to filter out the cholesterol in the blood figurativeyou’ll be put through to a secretary whose job it is to filter calls [no object, with adverbial of direction] move slowly or in small quantities or numbers through something or in a specified direction:people filtered out of the concert during the last set [no object, with adverbial] (of information) gradually become known:the news began to filter in from the hospital 2 Computing [with object] process or treat with a filter.