hypomagnesaemiaPronunciation: /ˌhʌɪpə(ʊ)ˌmagnɪˈziːmɪə/ (US hypomagnesemia)Definition of hypomagnesaemia noun [mass noun] Medicine & Veterinary Medicine deficiency of magnesium in the blood, important in cattle as the cause of grass tetany. Derivatives hypomagnesaemic adjective hypomagnesaemia in other Oxford dictionaries Definition of hypomagnesaemia in the US English dictionary