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.
      [1913 Webster]

   2. Hunched; hump-backed. [Obs.] --Sir T. Browne. --
      Gib"bous*ly, adv. -- Gib"bous*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

gibbous
    adj 1: characteristic of or suffering from kyphosis, an
           abnormality of the vertebral column [syn: crookback,
           crookbacked, humped, humpbacked, hunchbacked,
           gibbous, kyphotic]
    2: (used of the moon) more than half full [syn: gibbous,
       gibbose]

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "gibbous":
   arched, arciform, arclike, arcual, bandy, bowed, bowlike,
   bunchbacked, camelback, concave, convex, convexed, crookbacked,
   embowed, excurvate, excurvated, excurved, gibbose, humpbacked,
   humped, humpy, hunchbacked, hunched, hunchy, kyphotic, out-bowed,
   oxbow, rotund, vaulted