Tophus

from WordNet (r) 3.0 (2006)

tophus
    n 1: a deposit of urates around a joint or in the external ear;
         diagnostic of advanced or chronic gout [syn: {tophus},
         {chalkstone}]
    2: an incrustation that forms on the teeth and gums [syn:
       {tartar}, {calculus}, {tophus}]

from The Collaborative International Dictionary of English v.0.48

Tophus \To"phus\, n.; pl. {Tophi}. [NL.: cf. F. tophus a mineral
   concretion in the joint. See {Toph}.] [Written also {tofus}.]
   1. (Med.) One of the mineral concretions about the joints,
      and in other situations, occurring chiefly in gouty
      persons. They consist usually of urate of sodium; when
      occurring in the internal organs they are also composed of
      phosphate of calcium.
      [1913 Webster]

   2. (Min.) Calcareous tufa.
      [1913 Webster]