/ ˈfɪltə(r); NAmE / noun , verb
a device containing paper, sand, chemicals, etc. that a liquid or gas is passed through in order to remove any materials that are not wanted :
an air / oil filter
a coffee / water filter
filter paper for the coffee machine
He smokes cigarettes without filters.
—picture at cafetiere , laboratory
a device that allows only particular types of light or sound to pass through it
( computing ) a program that stops certain types of electronic information, email, etc. being sent to a computer
( BrE ) 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 wait
[ vn ] to pass liquid, light, etc. through a special device, especially to remove sth that is not wanted :
All drinking water must be filtered.
Use a sun block that filters UVA effectively.
( figurative )
My secretary is very good at filtering my calls (= making sure that calls that I do not want do not get through) .
—see also filtration
[ vn ] to use a special program to check the content of emails or websites before they are sent to your computer
[ v + adv. / prep. ] ( of people ) to move slowly in a particular direction :
The doors opened and people started filtering through.
[ v + adv. / prep. ] ( of information, news, etc. ) to slowly become known :
More details about the crash are filtering through.
[ v + adv. / prep. ] ( of light or sound ) to come into a place slowly or in small amounts :
Sunlight filtered in through the curtains.
[ v ] ( BrE ) ( of traffic at traffic lights ) to turn left at traffic lights while other vehicles wanting to go straight ahead or turn right must wait
- filter sth out
late Middle English (denoting a piece of felt): from French filtre , from medieval Latin filtrum felt used as a filter, of West Germanic origin and related to felt .