The Collaborative International Dictionary of English v.0.48:

Sovereign \Sov"er*eign\ (? or ?; 277), n.
   1. The person, body, or state in which independent and
      supreme authority is vested; especially, in a monarchy, a
      king, queen, or emperor.
      [1913 Webster]

            No question is to be made but that the bed of the
            Mississippi belongs to the sovereign, that is, to
            the nation.                           --Jefferson.
      [1913 Webster]

   2. A gold coin of Great Britain, on which an effigy of the
      head of the reigning king or queen is stamped, valued at
      one pound sterling, or about $4.86.
      [1913 Webster]

   3. (Zool.) Any butterfly of the tribe Nymphalidi, or genus
      Basilarchia, as the ursula and the viceroy.
      [1913 Webster]

   Syn: King; prince; monarch; potentate; emperor.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sovereign \Sov"er*eign\ (? or ?; 277), a. [OE. soverain,
   sovereyn, OF. soverain, suvrain, F. souverain, LL. superanus,
   fr. L. superus that is above, upper, higher, fr. super above.
   See Over, Super, and cf. Soprano. The modern spelling
   is due to a supposed connection with reign.]
   1. Supreme or highest in power; superior to all others;
      chief; as, our sovereign prince.
      [1913 Webster]

   2. Independent of, and unlimited by, any other; possessing,
      or entitled to, original authority or jurisdiction; as, a
      sovereign state; a sovereign discretion.
      [1913 Webster]

   3. Princely; royal. "Most sovereign name." --Shak.
      [1913 Webster]

            At Babylon was his sovereign see.     --Chaucer.
      [1913 Webster]

   4. Predominant; greatest; utmost; paramount.
      [1913 Webster]

            We acknowledge him [God] our sovereign good.
                                                  --Hooker.
      [1913 Webster]

   5. Efficacious in the highest degree; effectual; controlling;
      as, a sovereign remedy. --Dryden.
      [1913 Webster]

            Such a sovereign influence has this passion upon the
            regulation of the lives and actions of men. --South.
      [1913 Webster]

   Sovereign state, a state which administers its own
      government, and is not dependent upon, or subject to,
      another power.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sovereign
    adj 1: (of political bodies) not controlled by outside forces;
           "an autonomous judiciary"; "a sovereign state" [syn:
           autonomous, independent, self-governing,
           sovereign]
    2: greatest in status or authority or power; "a supreme
       tribunal" [syn: sovereign, supreme]
    n 1: a nation's ruler or head of state usually by hereditary
         right [syn: sovereign, crowned head, monarch]