obligate

verb

1. (transitive)To bind, compel, constrain, or oblige by a social, legal, or moral tie.

   “That progress has taken over ten years and £20 million to bring to fruition. But, as Mands explains, the journey has been one that HSG has been almost obligated to undertake. "First and foremost, this is an environmental project," she says.”

2. (Canada, Scotland, US, transitive)To cause to be grateful or indebted; to oblige.
3. (Canada, Scotland, US, transitive)To commit (money, for example) in order to fulfill an obligation.

adj

1. Requiring a (specified) way of life, habitat, etc.

   “[A]nalysis of the chemical composition of their bones reveals that they were obligate carnivores.”

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.”

   “Aquatic sites constitute obligate habitat for some species, and are critical breeding habitat for species with complex life cycles involving aquatic egg or larval development.”

   “Unlike for phagotrophic flagellates, bacteria serve as a facultative rather than an obligate food source for crustacean zooplankton.”

   “Light is the obligate energy source for the phototrophic microbes constructing these benthic mats”

3. (obsolete)Bound by oath, law or duty.

   “The Law sayith, Mack a mendis for thy synne. The Father of Heaven is wraith wyth thee. Quhair is thy rychteousnes, goodnes, and satisfactioun ? Thou art bound and obligat unto me, [to] the devill, and [to] hell.”

noun

1. An obligate organism.