An hotel's cocktail of alcohol (7)
I believe the answer is:
ethanol
'alcohol' is the definition.
(ethanol is a kind of alcohol)
'an hotel's cocktail' is the wordplay.
'cocktail' indicates anagramming the letters.
'an'+'hotel'='anhotel'
'anhotel' anagrammed gives 'ETHANOL'.
'of' acts as a link.
(Other definitions for ethanol that I've seen before include "porter uses it" , "Form of alcohol" , "Intoxicant in wine, spirits, etc" , "Ethyl alcohol" , "spirit" .)