The Collaborative International Dictionary of English v.0.48:

Multifariousness \Mul`ti*fa"ri*ous*ness\, n.
   1. Multiplied diversity.
      [1913 Webster]

   2. (Law) The fault of improperly uniting in one bill distinct
      and independent matters, and thereby confounding them.
      --Burrill.
      [1913 Webster]

WordNet (r) 3.0 (2006):

multifariousness
    n 1: noticeable heterogeneity; "a diversity of possibilities";
         "the range and variety of his work is amazing" [syn:
         diverseness, diversity, multifariousness, variety]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

MULTIFARIOUSNESS, equity pleading. By multifariousness in a bill, is
understood the improperly joining in one bill distinct matters, and thereby
confounding them; as, for example, the uniting in one bill, several matters,
perfectly distinct and unconnected, against one defendant; or the demand of
several matters of distinct natures, against several defendants in the same
bill. Coop. Eq. Pl. 182; Mitf. by Jeremy, 181; 2 Mason's R. 201; 18 Ves. 80;
Hardr. R. 337; 4 Cowen's R. 682; 4 Bouv. Inst. n. 4165.
     2. In order to prevent confusion in its pleadings and decrees, a court
of equity will anxiously discountenance this multifariousness. The following
case will illustrate this doctrine; suppose an estate should be sold in lots
to different persons, the purchasers could not join in exhibiting one bill
against the vendor for a specific performance; for each party's case would
be distinct, and would depend upon its own peculiar circumstances, and
therefore there should be a distinct bill upon each contract; on the other
hand, the vendor in the like case, would not be allowed to file one bill for
a specific performance against all the purchasers of the estate, for the
same reason. Coop. Eq. Pl. 182; 2 Dick. Rep. 677; 1 Madd. Rep. 88; Story's
Eq. Pl. Sec. 271 to 286. It is extremely difficult to say what constitutes
multifariousness as an abstract proposition. Story, Eq. Pl. Sec. 530, 539; 4
Blackf. 249; 2 How. S. C. Rep. 619, 642; 4 Bouv. Inst. n. 4243.