The Collaborative International Dictionary of English v.0.48:

Also \Al"so\, adv. & conj. [All + so. OE. al so, AS. ealsw[=a],
   alsw?, [ae]lsw[ae]; eal, al, [ae]l, all + sw[=a] so. See
   All, So, As.]
   1. In like manner; likewise. [Obs.]
      [1913 Webster]

   2. In addition; besides; as well; further; too.
      [1913 Webster]

            Lay up for yourselves treasures in heaven . . . for
            where your treasure is, there will your heart be
            also.                                 --Matt. vi.
                                                  20.
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   3. Even as; as; so. [Obs.] --Chaucer.
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   Syn: Also, Likewise, Too.

   Usage: These words are used by way of transition, in leaving
          one thought and passing to another. Also is the widest
          term. It denotes that what follows is all so, or
          entirely like that which preceded, or may be affirmed
          with the same truth; as, "If you were there, I was
          there also;" "If our situation has some discomforts,
          it has also many sources of enjoyment." Too is simply
          less formal and pointed than also; it marks the
          transition with a lighter touch; as, "I was there
          too;" "a courtier yet a patriot too." --Pope. Likewise
          denotes literally "in like manner," and hence has been
          thought by some to be more specific than also. "It
          implies," says Whately, "some connection or agreement
          between the words it unites. We may say, ` He is a
          poet, and likewise a musician; ' but we should not
          say, ` He is a prince, and likewise a musician,'
          because there is no natural connection between these
          qualities." This distinction, however, is often
          disregarded.
          [1913 Webster]

WordNet (r) 3.0 (2006):

also
    adv 1: in addition; "he has a Mercedes, too" [syn: besides,
           too, also, likewise, as well]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "also":
   above, additionally, again, all included, along, altogether,
   among other things, and, and all, and also, and so, as well,
   au reste, beside, besides, beyond, correspondingly, else, en plus,
   extra, farther, for lagniappe, further, furthermore, in addition,
   in like manner, inter alia, into the bargain, item, likewise, more,
   moreover, on the side, on top of, over, plus, similarly, so, still,
   then, therewith, to boot, too, vet, yea, yet