The Collaborative International Dictionary of English v.0.48:

Besides \Be*sides\, prep.
   Over and above; separate or distinct from; in addition to;
   other than; else than. See Beside, prep., 3, and Syn. under
   Beside.
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         Besides your cheer, you shall have sport. --Shak.
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The Collaborative International Dictionary of English v.0.48:

Besides \Be*sides"\, Beside \Be*side"\, adv. [OE. Same as
   beside, prep.; the ending -s is an adverbial one, prop. a
   genitive sign.]
   1. On one side. [Obs.] --Chaucer. Shak.
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   2. More than that; over and above; not included in the
      number, or in what has been mentioned; moreover; in
      addition.
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            The men said unto Lot, Hast thou here any besides ?
                                                  --Gen. xix.
                                                  12.
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            To all beside, as much an empty shade,
            An Eugene living, as a C[ae]sar dead. --Pope.
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   Note: These sentences may be considered as elliptical.
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WordNet (r) 3.0 (2006):

besides
    adv 1: making an additional point; anyway; "I don't want to go
           to a restaurant; besides, we can't afford it"; "she
           couldn't shelter behind him all the time and in any case
           he wasn't always with her" [syn: besides, in any
           case]
    2: in addition; "he has a Mercedes, too" [syn: besides, too,
       also, likewise, as well]