Source : Webster's Revised Unabridged Dictionary (1913)

Gibbous \Gib"bous\, a. [Cf. F. gibbeux. See {Gibbose}.]
   1. Swelling by a regular curve or surface; protuberant;
      convex; as, the moon is gibbous between the half-moon and
      the full moon.

            The bones will rise, and make a gibbous member.
                                                  --Wiseman.

   2. Hunched; hump-backed. [Obs.] --Sir T. Browne. --
      {Gib"bous*ly}, adv. -- {Gib"bous*ness}, n.

Source : WordNet®

gibbousness
     n : something that bulges out or is protuberant or projects from
         a form [syn: {bulge}, {bump}, {hump}, {gibbosity}, {jut},
          {prominence}, {protuberance}, {protrusion}, {extrusion},
          {excrescence}]