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]

Moby Thesaurus II by Grady Ward, 1.0:

98 Moby Thesaurus words for "inlet":
   access, adit, air lock, aisle, alley, ambulatory, aperture,
   approach, arcade, arm, artery, avenue, bay, bayou, bight,
   broaching, cavity, channel, chasm, check, clearing, cleft,
   cloister, colonnade, communication, conduit, connection, corridor,
   cove, covered way, crack, creek, defile, disclosure, entrance,
   entranceway, entry, entryway, exit, fenestra, ferry, fistula,
   fontanel, foramen, ford, gallery, gangplank, gangway, gap, gape,
   gat, gulf, hall, harbor, hiatus, hole, hollow, in, ingress, intake,
   interchange, intersection, interval, junction, lacuna, lane,
   laying open, leak, loch, lough, means of access, opening,
   opening up, orifice, outlet, overpass, pass, passage, passageway,
   pore, portico, railroad tunnel, slot, slough, space, split, stoma,
   throwing open, traject, trajet, tunnel, uncorking, underpass,
   unstopping, vestibule, way, way in, yawn