The Collaborative International Dictionary of English v.0.48:

Coactive \Co*ac"tive\, a. [In sense 1, fr. 1st Coact; in sense
   2, fr. 2d Coact.]
   1. Serving to compel or constrain; compulsory; restrictive.
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            Any coactive power or the civil kind. --Bp.
                                                  Warburton.
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   2. Acting in concurrence; united in action.
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            With what's unreal thou coactive art. --Shak.
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