I left insect eating radish top roughly (5)
I believe the answer is:
circa
'roughly' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for circa that I've seen before include "Costa del Sol city" , "About (a time)" , "Preceding a date, this means about" , "Close to" , "Preposition meaning about, usually preceding a date" .)