[ ˌmʌɪəs'θi:nɪə ]
(also ~ gravis 'grα:vɪs , 'gravɪs )
■ noun a rare chronic autoimmune disease marked by muscular weakness without atrophy.
Origin
C19: mod. L., from Gk mus 'muscle' + asthenia .
MYASTHENIA
Meaning of MYASTHENIA in English
Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004