The Collaborative International Dictionary of English v.0.48:
Mercaptan \Mer*cap"tan\, n. [F., fr. NL. mercurius mercury + L.
captans, p. pr. of captare to seize, v. intens. fr. capere.]
Any one of series of compounds having an -SH radical
attached to a carbon atom, also considered as 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.