The Collaborative International Dictionary of English v.0.48:

Costive \Cos"tive\ (k?s"t?v), a. [OF. costev['e], p. p. of
   costever, F. constiper, L. constipare to press closely
   together, to cram; con- + stipare to press together, cram.
   See Stipulate, Stiff, and cf. Constipate.]
   1. Retaining fecal matter in the bowels; having too slow a
      motion of the bowels; constipated.
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   2. Reserved; formal; close; cold. [Obs.] "A costive brain."
      --Prior. "Costive of laughter." --B. Jonson.
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            You must be frank, but without indiscretion; and
            close, but without being costive.     --Lord
                                                  Chesterfield.
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   3. Dry and hard; impermeable; unyielding. [Obs.]
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            Clay in dry seasons is costive, hardening with the
            sun and wind.                         --Mortimer.
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WordNet (r) 3.0 (2006):

costive
    adj 1: retarding evacuation of feces; binding; constipating
           [ant: laxative]