repulse vs fight off

repulse is a noun but fight off is not a noun.

Word	Noun	Adjective	Verb	Adverb
repulse	Yes	No	Yes	No
fight off	No	No	Yes	No

As verbs, repulse and fight off are synonyms defined as:

Other synonyms of repulse include drive back, rebuff, repel.

repulse (noun)	fight off (noun)
an instance of driving away or warding off

repulse (verb)	fight off (verb)
force or drive back	force or drive back
cause to move back by force or influence
be repellent to; cause aversion in