Initially attempt to oppose powers above (4)
I believe the answer is:
atop
'above' is the definition.
(thesaurus)
'initially attempt to oppose powers' is the wordplay.
'initially' says to take the initial letters.
The initial letters of 'attempt to oppose powers' is 'ATOP'.
(Other definitions for atop that I've seen before include "On (poetic)" , "Cooker heating element" , "On the highest point" , "In superior position" , "Positioned on" .)