1.NounA transitive verb, such as break, burn, boil, open, start, change, or assimilate, which may be used intransitively with the object of the action as the subject.
"The verb 'break' is labile because it can be used both transitively: I broke the window, and intransitively: the window broke, and in either case the object undergoing the action of breakage is the window."