The Collaborative International Dictionary of English v.0.48:

Inlet \In"let\, n.
   1. A passage by which an inclosed place may be entered; a
      place of ingress; entrance; especially, a narrow waterway
      leading into a harbor.
      [1913 Webster]

            Doors and windows, inlets of men and of light. --Sir
                                                  H. Wotton.
      [1913 Webster]

   2. A bay or recess, as in the shore of a sea, lake, or large
      river; a narrow strip of water running into the land or
      between islands.
      [1913 Webster]

   3. That which is let in or inlaid; an inserted material.
      [1913 Webster]

   Note: Inlet is also used adjectively, as in inlet pipe, inlet
         valve, etc.
         [1913 Webster]

WordNet (r) 3.0 (2006):

inlet
    n 1: an arm off of a larger body of water (often between rocky
         headlands) [syn: inlet, recess]
    2: an opening through which fluid is admitted to a tube or
       container [syn: intake, inlet]