The Collaborative International Dictionary of English v.0.48:

Incurvation \In`cur*va"tion\, n. [L. incurvatio: cf. F.
   incurvation.]
   [1913 Webster]
   1. The act of bending, or curving.
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   2. The state of being bent or curved; curvature.
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            An incurvation of the rays.           --Derham.
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   3. The act of bowing, or bending the body, in respect or
      reverence. "The incurvations of the knee." --Bp. Hall.
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WordNet (r) 3.0 (2006):

incurvation
    n 1: a shape that curves or bends inward [syn: concave shape,
         concavity, incurvation, incurvature]
    2: the action of creating a curved shape