Source : Webster's Revised Unabridged Dictionary (1913)

Supine \Su*pine"\, a. [L. supinus, akin to sub under, super
   above. Cf. {Sub-}, {Super-}.]
   1. Lying on the back, or with the face upward; -- opposed to
      prone.

   2. Leaning backward, or inclining with exposure to the sun;
      sloping; inclined.

            If the vine On rising ground be placed, or hills
            supine.                               --Dryden.

   3. Negligent; heedless; indolent; listless.

            He became pusillanimous and supine, and openly
            exposed to any temptation.            --Woodward.

   Syn: Negligent; heedless; indolent; thoughtless; inattentive;
        listless; careless; drowsy. -- {Su*pine"ly}, adv. --
        {Su*pine"ness}, n.

Source : WordNet®

supinely
     adv 1: with the face upward; "she was stretched supinely on her
            back"
     2: in an indifferently supine manner; "he called the tune to me
        and I supinely took it up"