Given the patient’s symptoms, I would say he_______has a serious infection.
Which of these commonly misspelled words is the CORRECT word and spelling for this sentence?

The word definitely is both the correct word and the correct spelling. Though each answer is similar to the proper spelling, each is flawed. Defiantly is an adjective used to describe doing something in a defiant manner, which does not fit the context of this sentence. Definately is an incorrect spelling of the word, and definitively is spelled correctly, but is the wrong word for the context of the sentence.