The Collaborative International Dictionary of English v.0.48:

Decussate \De*cus"sate\, v. t. [imp. & p. p. Decussated; p.
   pr. & vb. n. Decussating.] [L. decussatus, p. p. of
   decussare to cross like an X, fr. decussis (orig. equiv. to
   decem asses) the number ten, which the Romans represented by
   X.]
   To cross at an acute angle; to cut or divide in the form of
   X; to intersect; -- said of lines in geometrical figures,
   rays of light, nerves, etc. Decussate

The Collaborative International Dictionary of English v.0.48:

Decussate \De*cus"sate\, Decussated \De*cus"sa*ted\, a.
   1. Crossed; intersected.
      [1913 Webster]

   2. (Bot.) Growing in pairs, each of which is at right angles
      to the next pair above or below; as, decussated leaves or
      branches.
      [1913 Webster]

   3. (Rhet.) Consisting of two rising and two falling clauses,
      placed in alternate opposition to each other; as, a
      decussated period.
      [1913 Webster]

WordNet (r) 3.0 (2006):

decussate
    adj 1: crossed or intersected in the form of an X [syn:
           decussate, intersectant, intersecting]
    v 1: cross or intersect so as to form a cross; "this nerve
         decussates the other"; "the fibers decussate"