The Collaborative International Dictionary of English v.0.48:

Designment \De*sign"ment\, n.
   1. Delineation; sketch; design; ideal; invention. [Obs.]
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            For though that some mean artist's skill were shown
            In mingling colors, or in placing light,
            Yet still the fair designment was his own. --Dryden.
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   2. Design; purpose; scheme. [Obs.] --Shak.
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