Nouns

(n)mandatary, mandatorythe recipient of a mandate
(n)mandate, mandatorya territory surrendered by Turkey or Germany after World War I and put under the tutelage of some other European power until they are able to stand by themselves

Adjectives

(s)compulsory, mandatory, requiredrequired by rule“in most schools physical education is compulsory”, “attendance is mandatory”, “required reading”