ward off vs prevent

ward off and prevent both are verbs.

Word	Noun	Adjective	Verb	Adverb
ward off	No	No	Yes	No
prevent	No	No	Yes	No

As verbs, prevent is a hypernym of ward off; that is, prevent is a word with a broader meaning than ward off:

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

Other hypernyms of ward off include forbid, foreclose, forestall, preclude.

ward off (verb)	prevent (verb)
avert, turn away, or repel	stop (someone or something) from doing something or being in a certain state
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