The Collaborative International Dictionary of English v.0.48:

Tower \Tow"er\, v. i. [imp. & p. p. towered; p. pr. & vb. n.
   towering.]
   To rise and overtop other objects; to be lofty or very high;
   hence, to soar.
   [1913 Webster]

         On the other side an high rock towered still.
                                                  --Spenser.
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         My lord protector's hawks do tower so well. --Shak.
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The Collaborative International Dictionary of English v.0.48:

Towering \Tow"er*ing\, a.
   1. Very high; elevated; rising aloft; as, a towering height.
      --Pope.
      [1913 Webster]

   2. Hence, extreme; violent; surpassing.
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            A man agitated by a towering passion. --Sir W.
                                                  Scott.
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WordNet (r) 3.0 (2006):

towering
    adj 1: of imposing height; especially standing out above others;
           "an eminent peak"; "lofty mountains"; "the soaring spires
           of the cathedral"; "towering icebergs" [syn: eminent,
           lofty, soaring, towering]