C3H4OH.(CO2H)3

from The Collaborative International Dictionary of English v.0.48

Citric \Cit"ric\, a. [Cf. F. citrique. See {Citron}.] (Chem.)
   Of, pertaining to, or derived from, the citron or lemon; as,
   citric acid.
   [1913 Webster]

   {Citric acid} (Chem.), an organic acid, {C3H4OH.(CO2H)3},
      extracted from lemons, currants, gooseberries, etc., as a
      white crystalline substance, having a pleasant sour taste.
      [1913 Webster]