Synonyms: obligatory
Definition: morally or legally constraining or binding
Usage: attendance is obligatory; an obligatory contribution
Similar words: bounden
Definition: morally obligatory
Usage: my bounden duty
Similar words: compulsory, mandatory, required
Definition: required by rule
Usage: in most schools physical education is compulsory; attendance is mandatory; required reading
Similar words: de rigueur
Definition: required by etiquette or usage or fashion
Usage: instruction as to when and where a silk hat is de rigueur
Similar words: imposed
Definition: set forth authoritatively as obligatory
Usage: the imposed taxation; rules imposed by society
Similar words: incumbent on
Definition: morally binding or necessary
Usage: it is incumbent on me to attend
Similar words: indispensable
Definition: unavoidable
Usage: the routine but indispensable ceremonies of state
Similar words: prerequisite
Definition: required as a prior condition or course of study
Synonyms: obligatory
Definition: required by obligation or compulsion or convention
Usage: he made all the obligatory apologies
Similar words: necessary
Definition: absolutely essential