debar vs forestall

debar and forestall both are verbs.

Word	Noun	Adjective	Verb	Adverb
debar	No	No	Yes	No
forestall	No	No	Yes	No

As verbs, forestall is a hypernym of debar; that is, forestall is a word with a broader meaning than debar:

debar: prevent the occurrence of; prevent from happening; to protect from or to keep away anything undesirable; to ward off
forestall: keep from happening or arising; make impossible

Other hypernyms of debar include forbid, foreclose, preclude, prevent.

debar (verb)	forestall (verb)
prevent from entering; keep out	act in advance of; deal with ahead of time
prevent the occurrence of; prevent from happening; to protect from or to keep away anything undesirable; to ward off	keep from happening or arising; make impossible
bar temporarily; from school, office, etc.