In a clear way, oppose firm energetically (8)
I believe the answer is:
limpidly
'firm energetically' is the definition.
Both the definition and answer are adverbs. Perhaps they are linked in a way I don't understand?
'in a clear way oppose' is the wordplay.
I cannot quite see how this works, but
'clear' could be 'limpid' (similar in meaning) and 'limpid' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for limpidly that I've seen before include "clearly" , "calmly" .)