myotoniaPronunciation: /ˌmʌɪə(ʊ)ˈtəʊnɪə/Definition of myotonia noun [mass noun] Medicine inability to relax voluntary muscle after vigorous effort. Derivatives myotonicPronunciation: /-ˈtɒnɪk/ adjective Origin: late 19th century: from myo- 'muscle' + Greek tonos 'tone'myotonia in other Oxford dictionaries Definition of myotonia in the US English dictionary