1. a fuming liquid consisting of sulfuric acid with dissolved sulfur trioxide, used in chemical manufacturing and as a powerful oxidizing agent
Usage: chemistry; also called fuming sulfuric acid
2. in ancient Rome, a fragrant oil or perfume
Usage: archaic; historical

Examples

• Oleum is highly corrosive and must be handled with extreme care in the laboratory.
• The chemical plant uses oleum in the production of various industrial compounds.
• Oleum reacts vigorously with water and organic materials.
• Safety protocols require special containers for storing oleum.
• The concentration of sulfur trioxide in oleum determines its strength and reactivity.