obligatory

adj

1. Imposing obligation, legally, morally, or otherwise; binding; mandatory.

   “an obligatory promise”

   “[…] if he speak the words of an oath in a strange language, thinking they signify something else, or if he spake in his sleep, or deliration, or distraction, it is no oath, and so not obligatory.”

   “[I]t was something that every schoolboy of my generation almost `had' to do, as obligatory a proof of impending manliness as scrumping apples or pulling girls' pigtails.”

2. Requiring a matter or obligation.