obligatory
1. [ adjective ] required by obligation or compulsion or convention
Examples:

"he made all the obligatory apologies"

Related terms: necessary
2. [ adjective ] morally or legally constraining or binding
Examples:

"attendance is obligatory" "an obligatory contribution"

Related terms: optional compulsory imposed incumbent_on bounden indispensable prerequisite de_rigueur necessary
Similar spelling:   obligato
  obbligato
  obligatorily
  obligate
  obligated
  obligation
  obliger
  obligingly
  obliging
  obligational