Powerful agency about to take on a player (7)
I believe the answer is:
reactor
'powerful agency' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'about to take on a player' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'to take on' means one lot of letters go next to another.
'a player' becomes 'actor' ('actor' can be a synonym of 'player').
're'+'actor'='REACTOR'
Can you help me to learn more?
(Other definitions for reactor that I've seen before include "Producer of nuclear energy" , "nuclear facility" , "Heart of a nuclear power station" , "Atomic pile" , "See 3 Down" .)