Extraordinarily powerful article Poirot was on to (9)
I believe the answer is:
herculean
'extraordinarily powerful' is the definition.
'herculean' can be an answer for 'powerful' (synonyms). I am not certain of the 'extraordinarily' bit.
'article poirot was on to' is the wordplay.
I cannot quite see how this works, but
'article' could be 'an' (indefinite article) and 'an' is present in the answer.
'poirot' could be 'hercule' (Hercule Poirot) and 'hercule' is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for herculean that I've seen before include "Old Labour" , "Monumental (task)" , "Requiring very great effort" , "Enormously demanding (task)" , "Colossal" .)