To succeed in defeating a challenge, or an attack.(verb)
To resist, particularly an infection or an emotion.(verb)
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Use "fight off" in a sentence
"Omort cant fight off the alliance the Valkyrie Nx is forming."
"This new game, sold by Hasbro, the giant toy maker, appeals to kids to fight off an invasion by deadly extraterrestrials called Pox, who have escaped from a laboratory."
"Four thousand years ago, according to the earliest medical textbook ever discovered the Ebers Papyrus, found in the sands of Egypt, physicians were already using enemas to help the body cleanse and fight off disease."