The Collaborative International Dictionary of English v.0.48:

Tensor \Ten"sor\, n. [NL. See Tension.]
   1. (Anat.) A muscle that stretches a part, or renders it
      tense.
      [1913 Webster]

   2. (Geom.) The ratio of one vector to another in length, no
      regard being had to the direction of the two vectors; --
      so called because considered as a stretching factor in
      changing one vector into another. See Versor.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tensor
    n 1: a generalization of the concept of a vector
    2: any of several muscles that cause an attached structure to
       become tense or firm