Meaning

noun a chronic progressive disease characterized by chronic fatigue and muscular weakness (especially in the face and neck); caused by a deficiency of acetylcholine at the neuromuscular junctions

noun any muscular weakness

originFrom my- (“relating to muscle”) + asthenia (“weakness”), from Ancient Greek ἀσθένεια (asthéneia, “weakness”). By surface analysis, my- (“muscle”) + a- (“not”) + sthen- (“strength”) + -ia (“disease”).

Etymology from Wiktionary, CC BY-SA 3.0