The Collaborative International Dictionary of English v.0.48:

Infiltration \In`fil*tra"tion\, n. [Cf. F. infiltration.]
   [1913 Webster]
   1. The act or process of infiltrating, as of water into a
      porous substance, of a fluid into the cells of an organ or
      part of the body, or of persons into a hostile
      organization.
      [1913 Webster +PJC]

   2. The substance which has entered the pores or cavities of a
      body. --Addison.
      [1913 Webster]

            Calcareous infiltrations filling the cavities.
                                                  --Kirwan.
      [1913 Webster]

   Fatty infiltration. (Med.) See under Fatty.

   Infiltration gallery, a filter gallery.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Filter \Fil"ter\, n. [F. filtre, the same word as feutre felt,
   LL. filtrum, feltrum, felt, fulled wool, this being used for
   straining liquors. See Feuter.]
   Any porous substance, as cloth, paper, sand, or charcoal,
   through which water or other liquid may passed to cleanse it
   from the solid or impure matter held in suspension; a chamber
   or device containing such substance; a strainer; also, a
   similar device for purifying air.
   [1913 Webster]

   Filter bed, a pond, the bottom of which is a filter
      composed of sand gravel.

   Filter gallery, an underground gallery or tunnel, alongside
      of a stream, to collect the water that filters through the
      intervening sand and gravel; -- called also infiltration
      gallery.
      [1913 Webster]