American star ultimately injected huge power into parts (7)
I believe the answer is:
asunder
'into parts' is the definition.
(I've seen this in another clue)
'american star ultimately injected huge power' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'star' becomes 'sun' (the Sun is a star).
'ultimately' indicates one should take the final letters.
The final letters of 'injected huge power' are 'der'.
'a'+'sun'+'der'='ASUNDER'
(Other definitions for asunder that I've seen before include "being in two" , "going to pieces" , "(Rent) apart" , "Let no man put -" , "(Broken) apart" .)