Filter \Fil"ter\, v. t. [imp. & p. p. Filtered; p. pr. & vb. n. Filtering] [Cf. F. filter. See Filter, n., and cf. Filtrate.]

To purify or defecate, as water or other liquid, by causing it to pass through a filter.

Filtering paper, or Filter paper, a porous unsized paper, for filtering.

Source: Webster's Revised Unabridged Dictionary (1913)