“Noxious” is an adjective meaning “unpleasant”. It’s most often used to refer to an odor. Something that is noxious is quite often toxic as well – and there’s an extra x-word for you!

Example:  “We were cleaning out the drawers in his desk and accidentally opened an old carton of leftover food – the entire office was filled with the noxious odor of spoiled meat for days.”