Act artificially polite when cross within (7)
I believe the answer is:
'act' is the definition.
(exploit is a kind of act)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for exploit that I've seen before include "Benefit from" , "Capitalise on, take advantage of" , "Make full use of" , "Daring feat; use unfairly" , "Make use of - achievement" .)