inflammable air en · NOUN
Meanings
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(historical, uncountable) Hydrogen.
Mr. Cavendish has shewn, that the gas called inflammable air, is at least ten times lighter than common air; Mr. Lavoisier contends, that it is one of the component parts of water, and is by him called hydrogene.
1791, Erasmus Darwin, The Economy of Vegetation, J. Johnson, page 11: