mercaptan

noun

1. Any of a class of organic compounds of sulphur, ( R-SH ) where R represents an alkyl or other organic substituent. They tend to be foul-smelling. They are also termed thiols or thioalcohols.

   “Though this might come as a surprise, gas actually has no odor; gas companies are obligated to odorize it to make it safer for use in homes. Mercaptan, a harmless chemical, is added to create the distinct smell in both natural gas (methane) and liquid petroleum gas (propane, butane).”