Onset of myasthenia embodied by sharp tremor (7)
I believe the answer is:
tremble
'tremor' is the definition.
(synonyms)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tremble that I've seen before include "Shiver or jerk quickly" , "Betray nerves" , "Shiver slightly as with cold" , "Shake with fear or excitement" , "Shudder" .)