Longman Dictionary of Contemporary English homepage

Date: 1300-1400
Language: Old French
Origin: filtre 'piece of felt (= thick material) used as a filter', from Medieval Latin filtrum

filter

1 noun
     
fil‧ter1 [countable]
1T something that you pass water, air etc through in order to remove unwanted substances and make it clean or suitable to use
coffee filter papers
filter cigarettes (=with a filter at the end)
2TDC a piece of equipment or computer program that only allows certain sounds, images, signals, types of information etc to pass through it:
a UVA light filter
The firm uses electronic filters to prevent workers from accessing the Internet.
3 British EnglishTTC a traffic light that shows car drivers when they can turn right or left

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