The Collaborative International Dictionary of English v.0.48:

Farewell \Fare`well"\, interj. [Fare (thou, you) + well.]
   Go well; good-by; adieu; -- originally applied to a person
   departing, but by custom now applied both to those who depart
   and those who remain. It is often separated by the pronoun;
   as, fare you well; and is sometimes used as an expression of
   separation only; as, farewell the year; farewell, ye sweet
   groves; that is, I bid you farewell.
   [1913 Webster]

         So farewell hope, and with hope, farewell fear.
                                                  --Milton.
   [1913 Webster]

         Fare thee well! and if forever,
         Still forever fare thee well.            --Byron.
   [1913 Webster]

   Note: The primary accent is sometimes placed on the first
         syllable, especially in poetry.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Farewell \Fare`well"\, n.
   1. A wish of happiness or welfare at parting; the parting
      compliment; a good-by; adieu.
      [1913 Webster]

   2. Act of departure; leave-taking; a last look at, or
      reference to something.
      [1913 Webster]

            And takes her farewell of the glorious sun. --Shak.
      [1913 Webster]

            Before I take my farewell of the subject. --Addison.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Farewell \Fare"well`\, a.
   Parting; valedictory; final; as, a farewell discourse; his
   farewell bow.
   [1913 Webster]

         Leans in his spear to take his farewell view.
                                                  --Tickell.
   [1913 Webster]

   Farewell rock (Mining), the Millstone grit; -- so called
      because no coal is found worth working below this stratum.
      It is used for hearths of furnaces, having power to resist
      intense heat. --Ure.
      [1913 Webster]

WordNet (r) 3.0 (2006):

farewell
    n 1: an acknowledgment or expression of goodwill at parting
         [syn: farewell, word of farewell]
    2: the act of departing politely; "he disliked long farewells";
       "he took his leave"; "parting is such sweet sorrow" [syn:
       farewell, leave, leave-taking, parting]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "farewell":
   Godspeed, adieu, aloha, by, bye-bye, conge, departing, departure,
   doch-an-dorrach, final, good-bye, last, leave, leave-taking,
   leaving, outward-bound, parting, parting words, send-off, so long,
   stirrup cup, valediction, valedictorian, valedictory,
   valedictory address, viaticum