A substance or agent that causes asphyxia by preventing oxygen from reaching the body.
From 'asphyxia' plus the Latin suffix '-ant' (agent noun), meaning a substance that causes the condition of suffocation.
Nitrogen is technically an asphyxiant—it's not poisonous at all, but it'll kill you by displacing oxygen, which is why it's the most underestimated dangerous gas in laboratories.
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