prohibitive adj.

early 15c., prohibitif, "having the quality of prohibiting, serving to forbid," from Medieval Latin prohibitivus, from prohibit-, past-participle stem of Latin prohibere "hold back, restrain, hinder, prevent" (see prohibit). Of prices, rates, etc., "so high as to prevent use," it is from 1886. Related: Prohibitively. Alternative prohibitory (1590s) is from Latin prohibitorius.