1a device containing paper, sand, chemicals, etc. that a liquid or gas is passed through in order to remove any materials that are not wantedan air/oil filtera coffee/water filterfilter paper for the coffee machineHe smokes cigarettes without filters.2a device that allows only particular types of light or sound to pass through itThe camera has an anti-glare filter.3(computing) a program that stops certain types of electronic information, email, etc. being sent to a computer4(British English) a light on a set of traffic lights showing that traffic can turn left or right while traffic that wants to go straight ahead must waita filter lane
ˈfɪltə(r)
ˈfɪltər