The Collaborative International Dictionary of English v.0.48:

Almighty \Al*might"y\ ([add]l*m[imac]t"[y^]), a. [AS. ealmihtig,
   [ae]lmihtig; eal (OE. al) all + mihtig mighty.]
   1. Unlimited in might; omnipotent; all-powerful;
      irresistible.
      [1913 Webster]

            I am the Almighty God.                --Gen. xvii.
                                                  1.
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   2. Great; extreme; terrible. [Slang]
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            Poor Aroar can not live, and can not die, -- so that
            he is in an almighty fix.             --De Quincey.
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   The Almighty, the omnipotent God. --Rev. i. 8.
      [1913 Webster]

WordNet (r) 3.0 (2006):

almighty
    adj 1: having unlimited power [syn: almighty, all-powerful,
           omnipotent]
    n 1: terms referring to the Judeo-Christian God [syn: Godhead,
         Lord, Creator, Maker, Divine, God Almighty,
         Almighty, Jehovah]