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1. Offensive to the point of arousing disgust; foul: a noisome odor.
2. Harmful or dangerous: noisome fumes.
[Middle English noiesom : noie, harm (short for anoi, annoyance, from Old French, from anoier, to annoy; see annoy) + -som, adj. suff.; see -some1.]
Usage Note: People sometimes assume that noisome means "noisy," because the two words sound similar. But in our 2011 survey, 89% of the Usage Panel found the sentence We could barely hear each other with the noisome helicopter overhead to be unacceptable. If you use noisome as a synonym for noisy, there's a good chance that others will misinterpret your words and think you're describing someone or something as being offensive or harmful.