sulfur trioxide

noun

: a compound SO₃ that is a heavy low-boiling strongly acid corrosive liquid when first produced at ordinary temperatures but that polymerizes readily to three or more solid forms including a stable modification resembling asbestos, that is formed by the union of sulfur dioxide and oxygen (as in the contact process for making sulfuric acid) but is usually made by distillation of strong oleum, that gives off irritating toxic fumes in air and combines violently with water evolving much heat and forming sulfuric acid, that is a powerful oxidizing agent and sets fire to materials like excelsior and sawdust on contact, and that is used chiefly as a sulfonating and sulfating agent (as in making detergents)

Love words?

You must — there are over 200,000 words in our free online dictionary, but you are looking for one that’s only in the Merriam-Webster Unabridged Dictionary.

Start your free trial today and get unlimited access to America's largest dictionary, with:

• More than 250,000 words that aren't in our free dictionary
• Expanded definitions, etymologies, and usage notes
• Advanced search features
• Ad free!