fil·ter 
(fĭltər)
(fĭltər)n.
1.
a. A porous material through which a liquid or gas is passed in order to separate the fluid from suspended particulate matter.
b. A device containing such a material, especially one used to extract impurities from air or water.
2.
a. Any of various electric, electronic, acoustic, or optical devices used to reject signals, vibrations, or radiations of certain frequencies while allowing others to pass.
b. A colored glass or other transparent material used to select the wavelengths of light allowed to reach a photosensitive material.
3. Computers A program or device that blocks email or restricts website access when specific criteria are met.
4. Informal The ability or tendency to censor oneself, as to avoid causing embarrassment or offense: My roommate has no filter and says whatever he's thinking at the moment.
v. fil·tered, fil·ter·ing, fil·ters
v.tr.
1. To pass (a liquid or gas) through a filter.
2. To remove by passing through a filter: filter out impurities.
3. Computers To use a filter to block or restrict access to: a program that filters spam.
4. Informal To censor (oneself), as to avoid causing embarrassment or offense.
v.intr.
1. To pass through or as if through a filter: Light filtered through the blinds.
2. To come or go gradually and in small groups: The audience filtered back into the hall.
[Middle English filtre, from Old French, from Medieval Latin filtrum, of Germanic origin; see pel-5 in the Appendix of Indo-European roots.]
filter·er n.
filter·less adj.