mustard gas

WordReference Random House Learner's Dictionary of American English © 2025

ˈmus•tard ˌgas, n. [uncountable]

1. Chemistry an oily liquid, used, esp. in World War I, as a chemical-warfare gas.

WordReference Random House Unabridged Dictionary of American English © 2025

mus′tard gas′, 

1. Chemistry an oily liquid, C₄H₈Cl₂S, used as a chemical-warfare gas, blistering the skin and damaging the lungs, often causing blindness and death: introduced by the Germans in World War I. Also called dichlorodiethyl sulfide. 

• so called from its mustard-like odor 1915–20

Collins Concise English Dictionary © HarperCollins Publishers::

mustard gas noun

1. an oily liquid vesicant compound used in chemical warfare. Its vapour causes blindness and burns. Formula: (ClCH₂CH₂)₂S