obligatory 10 Associations

bounden (similar term) compulsory (similar term) mandatory (similar term) required (similar term) de rigueur (similar term) imposed (similar term) incumbent on (similar term)

superjacent 11 Associations

incumbent (similar term) overlying (similar term) superimposed (similar term) superincumbent (similar term) subjacent (antonym)

voluntary 9 Associations

by choice (similar term) intentional (similar term) willful (similar term) wilful (similar term) freewill (similar term) self-imposed (similar term) uncoerced (similar term)