Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
praescriptīvus, a, um, adj. [praescribo, II. B.], of or relating to a legal exception or demurrer (post-class.): praescriptivae quaestiones, Jul. Vict. Art. Rhet. 3, 10: quaestiunculae, id. ib. 4, 1: praescripti vum praecedens, Sulp. Viet. Inst. Or. p. 282.
Adv.: praescriptīvē, with an exception (eccl. Lat.): occurrere, Tert. adv. Marc. 4, 1.