Deny, e.g., King Edward overthrown (5)
I believe the answer is:
rebut
'deny e g' is the definition.
'rebut' can be an answer for 'deny' (to rebut is to deny or refute). I am not certain of the 'e g' bit.
'king edward overthrown' is the wordplay.
'king edward' becomes 'tuber' (King Edward is a type of potato).
'overthrown' says the letters should be written in reverse.
'tuber' in reverse letter order is 'REBUT'.
Can you help me to learn more?
(Other definitions for rebut that I've seen before include "Deny claim" , "Contradict or disprove" , "Drive back" , "Refure or disprove" , "Prove to be false or incorrect" .)