Source : Webster's Revised Unabridged Dictionary (1913)

Preclusion \Pre*clu"sion\, n. [L. praeclusio. See {Preclude}.]
   The act of precluding, or the state of being precluded; a
   shutting out.

Source : WordNet®

preclusion
     n : the act of preventing something by anticipating and
         disposing of it effectively [syn: {obviation}, {forestalling}]