his ‧ ta ‧ mine /ˈhɪstəmiːn/ BrE AmE noun [uncountable and countable] medical
[ Date: 1900-2000 ; Origin: histidine 'type of amino acid' (19-21 centuries) (from Greek histos 'web, tissue' ) + amine 'type of chemical compound' (19-21 centuries) (from ammonia ) ]
a chemical substance produced by your body during an ↑ allergic reaction ⇨ antihistamine