Definitions of filter:

• noun:   device that removes something from whatever passes through it
• noun:   an electrical device that alters the frequency spectrum of signals passing through it
• verb:   remove by passing through a filter

  Example: "Filter out the impurities"

• verb:   run or flow slowly, as in drops or in an unsteady stream
• verb:   pass through
• name:  A surname (very rare: popularity rank in the U.S.: #33816)