n. & v.
n. 1 a porous device for removing impurities or solid particles from a liquid or gas passed through it. 2 = filter tip. 3 a screen or attachment for absorbing or modifying light, X-rays, etc. 4 a device for suppressing electrical or sound waves of frequencies not required. 5 Brit. a an arrangement for filtering traffic. b a traffic-light signalling this.
v.intr. & tr. 1 pass or cause to pass through a filter. 2 (foll. by through, into, etc.) make way gradually. 3 (foll. by out) leak or cause to leak. 4 Brit. allow (traffic) or (of traffic) be allowed to pass to the left or right at a junction while traffic going straight ahead is halted (esp. at traffic lights). filter-bed a tank or pond containing a layer of sand etc. for filtering large quantities of liquid. filter-paper porous paper for filtering. filter tip 1 a filter attached to a cigarette for removing impurities from the inhaled smoke. 2 a cigarette with this. filter-tipped having a filter tip.
[ F filtre f. med.L filtrum felt used as a filter, f. WG ]