The Collaborative International Dictionary of English v.0.48:

Commixture \Com*mix"ture\ (?; 135), n. [L. commixtura.]
   1. The act or process of mixing; the state of being mingled;
      the blending of ingredients in one mass or compound.
      [1913 Webster]

            In the commixture of anything that is more oily or
            sweet, such bodies are least apt to putrefy.
                                                  --Bacon.
      [1913 Webster]

   2. The mass formed by mingling different things; a compound;
      a mixture. --Bacon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

commixture
    n 1: the act of mixing together; "paste made by a mix of flour
         and water"; "the mixing of sound channels in the recording
         studio" [syn: mix, commixture, admixture, mixture,
         intermixture, mixing]