filter

1 noun (C)

1 a piece of equipment or a substance that you pass gas or liquid through to remove unwanted substances: a water filter

2 a piece of glass or plastic that changes the amount or colour of light allowed into a camera or telescope 1

3 a piece of equipment that only allows certain sounds to pass through it

4 BrE a light used to tell drivers they can turn right or left

2 verb

1 (T) to clean a liquid or gas by passing it through a special substance or piece of equipment: You need to filter the drinking water.

2 (intransitive always + adv/prep) if people filter somewhere, they move gradually in that direction through a door, passage etc

(+ in/out etc): Chattering noisily, the crowd began to filter into the auditorium.

3 (intransitive always + adv/prep) if news or information filters somewhere, people gradually hear about it from each other

(+ back/through etc): The news slowly filtered through to everyone in the office.

4 (intransitive always + adv/prep) if light or sound filters into a place, it can be seen or heard only slightly

(+ in/into/through): A few rays of sunshine filtered into the cave.

5 (I) BrE if traffic filters, cars can turn left or right while other vehicles going straight ahead must wait

filter sth out phrasal verb (T) to remove something by using a filter: The machine filters out sediment.