The Collaborative International Dictionary of English v.0.48:

Rachitis \Ra*chi"tis\ (r[.a]*k[imac]"t[i^]s), n. [NL., fr. Gr.
   "rachi^tis (sc. nosos), fr. "ra`chis, -ios, the spine.]
   [Written also rhachitis.]
   1. (Med.) Literally, inflammation of the spine, but commonly
      applied to the rickets. See Rickets.
      [1913 Webster]

   2. (Bot.) A disease which produces abortion in the fruit or
      seeds. --Henslow.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rickets \Rick"ets\, n. pl. [Of uncertain origin; but cf. AS.
   wrigian to bend, D. wrikken to shake, E. wriggle.] (Med.)
   A disease which affects children, and which is characterized
   by a bulky head, crooked spine and limbs, depressed ribs,
   enlarged and spongy articular epiphyses, tumid abdomen, and
   short stature, together with clear and often premature mental
   faculties. The essential cause of the disease appears to be
   the nondeposition of earthy salts in the osteoid tissues.
   Children afflicted with this malady stand and walk
   unsteadily. Called also rachitis.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rachitis
    n 1: inflammation of the vertebral column
    2: childhood disease caused by deficiency of vitamin D and
       sunlight associated with impaired metabolism of calcium and
       phosphorus [syn: rickets, rachitis]