Real Dictionary

gerundive in American English
in Latin, a verbal adjective with a typical gerund stem form, used as a future passive participle expressing duty, necessity, fitness, etc. (Ex.: delenda in delenda est Carthago, “ Carthage must be destroyed”)
adjective: resembling a gerund
noun: a verbal adjective similar to the gerund in form and noting the obligation, necessity, or worthiness of the action to be done, as legendus in Liber legendus est, “The book is worth reading”

gerundive in British English
adjective: of or relating to the gerund or gerundive
noun: (in Latin grammar) an adjective formed from a verb, expressing the desirability of the activity denoted by the verb