Source : Webster's Revised Unabridged Dictionary (1913)

Prescriptive \Pre*scrip"tive\, a. [L. praescriptivus of a
   demurrer or legal exception.] (Law)
   Consisting in, or acquired by, immemorial or long-continued
   use and enjoyment; as, a prescriptive right of title;
   pleading the continuance and authority of long custom.

         The right to be drowsy in protracted toil has become
         prescriptive.                            --J. M. Mason.

Source : WordNet®

prescriptive
     adj 1: giving directives or rules; "prescriptive grammar is
            concerned with norms of or rules for correct usage"
            [syn: {normative}] [ant: {descriptive}]
     2: based on or prescribing a norm or standard; "normative
        grammar" [syn: {normative}]