obligate

Short definition from Wiktionary

Verb

1. 1
   To bind, compel, constrain, or oblige by a social, legal, or moral tie.
2. 2
   To cause to be grateful or indebted; to oblige.
3. 3
   To commit (money, for example) in order to fulfill an obligation.

Adjective

1. 1
   Requiring a (specified) way of life, habitat, etc.
2. 2
   Indispensable; essential; necessary; obligatory; mandatory; unavoidably invoked.