obligate

ob·li·gate

adj \ˈäb-li-gət, -lə-ˌgāt\

Definition of OBLIGATE

1

: restricted to one particularly characteristic mode of life or way of functioning <the infant is an obligate nose breather—Journal of the American Medical Association> <an obligate parasite>

2

: biologically essential for survival <obligate parasitism>

—ob·li·gate·ly adverb