noun

a porous device for removing impurities or solid particles from a liquid or gas passed through it.

an oil filter

strainer,sifter,sieve,riddle,colander,gauze,netting

verb

pass (a liquid, gas, light, or sound) through a device to remove unwanted material.

the eye filters out ultraviolet radiation

sieve,strain,sift,filtrate,riddle,clarify,purify,clear,clean,make pure,refine,treat,process,decontaminate