Definify.com
Webster 1913 Edition
Ethylsulphuric
Ethˊyl-sul-phu′ric
Adj.
 (Chem.) 
Pertaining to, or containing, ethyl and sulphuric acid. 
Ethylsulphuric acid 
(Chem.)
, an acid sulphate of ethyl, 
 H.C2H5.SO4
, produced as a thick liquid by the action of sulphiric acid on alcohol. It appears to be the active catalytic agent in the process of etherification.