pre ‧ scrip ‧ tive /prɪˈskrɪptɪv/ BrE AmE adjective
1 . saying how something should or must be done, or what should be done:
prescriptive teaching methods
2 . stating how a language should be used, rather than describing how it is used OPP descriptive :
prescriptive grammar
3 . prescriptive right British English law a right that has existed for so long that it is as effective as a law
—prescriptively adverb