Mercaptan \Mer*cap"tan\, n. [F., fr. NL. mercurius mercury + L. captans, p. pr. of captare to seize, v. intens. fr. capere.]

(Chem.) Any one of series of compounds, hydrosulphides of alcohol radicals, in composition resembling the alcohols, but containing sulphur in place of oxygen, and hence called also the sulphur alcohols. In general, they are colorless liquids having a strong, repulsive, garlic odor. The name is specifically applied to ethyl mercaptan, C2H5SH. So called from its avidity for mercury, and other metals.

Source: Webster's Revised Unabridged Dictionary (1913)