A person who belittles the worth of another person or cause.(noun)
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Use "detractor" in a sentence
"The only detractor is the metal detector in the lobby."
"On the other side of the debate is Ed Dwight, a long-term detractor."
"Oil, and all that it means to us at this time, has a great deal to do with the number one detractor from the business environment of the moment, and that is automobile sales."