noun

1. a device for separating solid particles, impurities, etc. from a liquid or gas by passing it through a porous substance
2. any porous substance used or suitable for this, as sand, charcoal, felt, etc.
3. Physics
   1. a device or substance that passes electric currents of certain frequencies or frequency ranges while preventing the passage of others
   2. a device or substance that partially or completely absorbs certain light rays a color filter for a camera lens

Etymology: ME filtre < OFr < ML filtrum, feltrum, felt, fulled wool (used for straining liquors) < Gmc: see felt

transitive verb

1. to pass (a liquid or gas) through a filter
2. to remove or separate (solid particles, impurities, etc.) from a liquid or gas by means of a filter: often with out
3. to act as a filter for

Etymology: Fr filtrer < the n.

intransitive verb

1. to pass through or as if through a filter
2. to move or pass slowly the news filtered through town