The Collaborative International Dictionary of English v.0.48:

Attention \At*ten"tion\, n. [L. attentio: cf. F. attention.]
   1. The act or state of attending or heeding; the application
      of the mind to any object of sense, representation, or
      thought; notice; exclusive or special consideration;
      earnest consideration, thought, or regard; obedient or
      affectionate heed; the supposed power or faculty of
      attending.
      [1913 Webster]

            They say the tongues of dying men
            Enforce attention like deep harmony.  --Shak.
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   Note: Attention is consciousness and something more. It is
         consciousness voluntarily applied, under its law of
         limitations, to some determinate object; it is
         consciousness concentrated. --Sir W. Hamilton.
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   2. An act of civility or courtesy; care for the comfort and
      pleasure of others; as, attentions paid to a stranger.
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   To pay attention to, To pay one's attentions to, to be
      courteous or attentive to; to wait upon as a lover; to
      court.
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   Syn: Care; heed; study; consideration; application;
        advertence; respect; regard.
        [1913 Webster]

WordNet (r) 3.0 (2006):

attention
    n 1: the process whereby a person concentrates on some features
         of the environment to the (relative) exclusion of others
         [syn: attention, attending] [ant: inattention]
    2: the work of providing treatment for or attending to someone
       or something; "no medical care was required"; "the old car
       needs constant attention" [syn: care, attention, aid,
       tending]
    3: a general interest that leads people to want to know more;
       "She was the center of attention"
    4: a courteous act indicating affection; "she tried to win his
       heart with her many attentions"
    5: the faculty or power of mental concentration; "keeping track
       of all the details requires your complete attention"
    6: a motionless erect stance with arms at the sides and feet
       together; assumed by military personnel during drill or
       review; "the troops stood at attention"