bounden 7 Associations

obligatory (similar term)

compulsory 10 Associations

mandatory required obligatory (similar term)

de rigueur 10 Associations

obligatory (similar term)

imposed 7 Associations

obligatory (similar term)

incumbent on 12 Associations

obligatory (similar term)

indispensable 13 Associations

obligatory (similar term)

mandatory 9 Associations

compulsory required obligatory (similar term)

optional 8 Associations

elective (similar term) ex gratia (similar term) facultative (similar term) nonmandatory (similar term) nonobligatory (similar term) obligatory (antonym)

prerequisite 12 Associations

obligatory (similar term)

required 8 Associations

compulsory mandatory obligatory (similar term)