Almighty muddle in poem not finally relevant (10)
I believe the answer is:
omnipotent
'almighty' is the definition.
(I know that almighty can be written as omnipotent)
'muddle in poem not finally relevant' is the wordplay.
'muddle' is an anagram indicator.
'finally' suggests the final letters.
The final letter of 'relevant' is 't'.
'in'+'poem'+'not'='inpoemnot'
'inpoemnot' anagrammed gives 'omnipoten'.
'omnipoten'+'t'='OMNIPOTENT'
(Other definitions for omnipotent that I've seen before include "All-powerful" , "Almighty" .)