The Collaborative International Dictionary
ethyl mercaptan
ethyl mercaptan \eth"yl mer*cap"tan\, (Chem.) A gaseous substance ( C2H5.SH) used as an odorant in natural gas and propane to facilitate detection and serve as a warning of leaks.
Wiktionary
ethyl mercaptan
n. (context organic compound English) a thiol formally derived from ethyl alcohol by replacing the oxygen atom with sulfur