obligate (
http://definr.com/obligate)
adj 1: (biology) restricted to a particular condition of life; "an
obligate anaerobe can survive only in the absence of
OXYGen" [ant:
facultative]
2: being under moral or legal obligation; "felt bound by his
promise" [syn:
bound,
compelled(p),
constrained(p)]
v : force or compel somebody to do something; "We compel all
students to fill out this form" [syn:
compel,
oblige]