obligate
verb
Definitions
To bind, compel, constrain, or oblige by a social, legal, or moral tie.
To cause to be grateful or indebted; to oblige.
To commit (money, for example) in order to fulfill an obligation.
adjective
Definitions
Able to exist or survive only in a particular environment or by assuming a particular role.
Example: an obligate anaerobe
Absolutely indispensable; essential.