obligate

باللغة العربية: إِجْباريّ، مُلْزِم

1. Requiring a (specified) way of life, habitat, etc.
2. Indispensable; essential; necessary; obligatory; mandatory; unavoidably invoked. · In addition to being the obligate food source for monarch caterpillars, milkweeds also provide abundant nectar for the adult butterflies.· In some languages such signaling is optional, whereas in others it is obligate.