To bind by moral or legal obligation.
To bind, compel, constrain, or oblige by a social, legal, or moral tie.
To commit (money, for example) in order to fulfill an obligation.
To cause to be grateful or indebted; to oblige.
Requiring a (specified) way of life, habitat, etc..
Indispensable; essential; necessary; obligatory; mandatory; unavoidably invoked.