形容词

1. （按照规定或法律）必须履行的，强制性的
If something is obligatory, you must do it because of a rule or a law.

2. 习惯性的;礼节性的;随大溜的
If you describe something as obligatory, you mean that it is done from habit or custom and not because the person involved has thought carefully about it or really means it.

1. morally or legally constraining or binding

e.g. attendance is obligatory
an obligatory contribution

2. required by obligation or compulsion or convention

e.g. he made all the obligatory apologies