nitrous oxide
noun/ˌnaɪtrəs ˈɒksaɪd/
/ˌnaɪtrəs ˈɑːksaɪd/
(also informal laughing gas)
[uncountable]- a gas used especially in the past by dentists to prevent you from feeling pain
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nitrous oxide
Definition of nitrous oxide noun from the Oxford Advanced Learner's Dictionary