Copper taking time to work secretly with a caterpillar (7)
I believe the answer is:
cutworm
'caterpillar' is the definition.
(I know that cutworm is a type of caterpillar)
'copper taking time to work secretly' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'taking' says to put letters next to each other.
'time' becomes 't' (abbreviation).
'to work' becomes 'w' (physics abbreviation).
'secretly' becomes 'orm' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'cu'+'t'+'w'+'orm'='CUTWORM'
'with a' is the link.
Can you help me to learn more?
(Other definitions for cutworm that I've seen before include "Caterpillar" , "Form of insect" , "pernicious type" .)