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1540s, "to bind, connect;" 1660s, "to put under moral obligation," back-formation from obligation, or else from Latin obligatus, past participle of obligare (see oblige). Oblige, with which it has been confused since late 17c., means "to do one a favor." Related: Obligated; obligating.
obligate ob·li·gate (ŏb'lĭ-gĭt, -gāt')
Able to exist or survive only in a particular environment or by assuming a particular role.
Capable of existing only in a particular environment or by assuming a particular role. An obligate aerobe, such as certain bacteria, can live only in the presence of oxygen. An obligate parasite cannot survive independently of its host. Compare facultative.