The Collaborative International Dictionary of English v.0.48:

Occlusion \Oc*clu"sion\, n. [See Occlude.]
   1. The act of occluding, or the state of being occluded.
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            Constriction and occlusion of the orifice. --Howell.
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   2. (Med.) The transient approximation of the edges of a
      natural opening; imperforation. --Dunglison.
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   Occlusion of gases (Chem. & Physics), the phenomenon of
      absorbing gases, as exhibited by platinum, palladium,
      iron, or charcoal; thus, palladium absorbs, or occludes,
      nearly a thousand times its own volume of hydrogen, and in
      this case a chemical compound seems to be formed.
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