methacholine
noun
metha·cho·line
| \ ˌmeth-ə-ˈkō-ˌlēn
\
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Medical Definition of methacholine
: a parasympathomimetic drug administered in the form of its crystalline chloride C8H18ClNO2 especially to diagnose hypersensitivity of the bronchial air passages (as in asthma) — see mecholyl, provocholine