Take command of moneylending business, assuming power for years (5)
I believe the answer is:
usurp
'take command' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for usurp that I've seen before include "Take over occupation" , "Oust" , "Seize power without authority" , "Seize power illegally" , "Commandeer" .)