Dismissed for being enthusiastic (5)
I believe the answer is:
fired
'dismissed' is the definition.
('fire' can be a synonym of 'dismiss')
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for fired that I've seen before include "sent up in flames" , "Stimulated; dismissed" , "(Of pottery) baked" , "Aroused" , "with P45?" .)