1) Ending for lin or rust 2) Fuming sulfuric acid 3) Oil in old Rome 4) Oil, pharmaceutically 5) Oil, to Ovid 6) Pharmaceutical oil 
Oleum (Latin oleum = `oil`), or fuming sulfuric acid, is a solution of various compositions of sulfur trioxide in sulfuric acid, or sometimes more specifically to disulfuric acid (also known as pyrosulfuric acid). Oleums can be described by the formula ySO3.H2O where y is the total molar sulfur trioxide content. The value of y can be varied, to .....
Fuming sulfuric acid
oleum (singular), olea (plural) A solution of sulfur trioxide in sulfuric acid.