(Latin: tie, bind)

Pertaining to, of the nature of, or forming a ligament.
ligamentous, ligamentously
Referring to or of the nature of a ligament.
ligamentum (s), ligamenta (pl)
The application of a ligature.
1. The process of binding or tying.
2. A band or bandage.
3. A thread or wire for tying a blood vessel or other structure in order to constrict or fasten it.
4. Etymology: "something used in tying or binding", from Old French ligature, from Late Latin ligatura, "a band", from Latin ligatus; past participle of ligare, "to bind".
Meckel ligament
Meckel band, the portion of the anterior ligament of the malleus that extends from the base of the anterior process through the petrotympanic fissure, to attach to the spine of the sphenoid.
obligate (adjective)
Restricted to a single or particular mode of behavior or environmental condition; such as, an obligate aerobe that is dependent on the presence of molecular oxygen in order to breathe.
obligate (verb), obligates; obligated; obligating
1. To bind, to compel, or to constrain by a social, legal, or moral tie.
2. To cause to be grateful or indebted; to oblige.
3. To commit; for example, money, in order to fulfill an obligation.
4. Etymology: from Latin "to bind by oath", from Old French obligier, from Latin obligare; from ob-, "to" + ligare, "to bind".
obligate aerobe, obligate aerobium (s) (noun); obligate aerobes; obligate aerobia (pl)
An organism that requires air or free oxygen for life: Obligate aerobes are dependent on molecular oxygen to breathe and to metabolize elements, like fats or sugars, in order to acquire energy.
obligate anaerobe (s) (noun), obligate anaerobes (pl)
An organism that can live only in the absence of oxygen: In comparison to an aerobe, obligate anaerobes are life forms, like some bacteria, that can only thrive in environments lacking free oxygen or air.
obligate carnivore, obligatory carnivore (true carnivore)
1. An animal that requires meat, or other animal products, in its diet in order to obtain the nutrients that are found in sufficient quantities.
2. An obligate, or true carnivore, is an animal that subsists on a diet consisting almost exclusively of meat.

They may consume other products presented to them, especially animal products like cheese and bone marrow or sweet sugary substances like honey and syrup; but, as these items are not essential they do not consume them on a regular basis.

True carnivores lack the physiology required for efficient digestion of vegetable matter; in fact, some carnivorous mammals eat vegetation matter specifically just as an emetic (for vomiting).

—As seen at Wikipedia

3. An animal that by its genetic makeup must eat the tissue of other animals in order to thrive.

Obligate carnivores may eat other foods; such as, vegetables, grains, or fruit, but they must eat meat as the main source for their nutrients.

obligate parasite
An organism that can exist only as a parasite.
obligate predator
A predator that is narrowly restricted to a specific kind of prey.
obligate saprophyte
An organism which can only live off dead organic matter. These fungi are very important as decomposers of organic material.
obligate symbionts
An organism that cannot function unless it is combined with another organism.