The Collaborative International Dictionary of English v.0.48:

Gibbous \Gib"bous\, a. [Cf. F. gibbeux. See Gibbose.]
   [1913 Webster]
   1. Swelling by a regular curve or surface; protuberant;
      convex; as, the moon is gibbous between the half-moon and
      the full moon.
      [1913 Webster]

            The bones will rise, and make a gibbous member.
                                                  --Wiseman.
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   2. Hunched; hump-backed. [Obs.] --Sir T. Browne. --
      Gib"bous*ly, adv. -- Gib"bous*ness, n.
      [1913 Webster]