Clever copper starts to teach experts (4)
I believe the answer is:
cute
'clever' is the definition.
(thesaurus)
'copper starts to teach experts' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'starts to' indicates taking the first letters.
The initial letters of 'teach experts' is 'te'.
'cu'+'te'='CUTE'
(Other definitions for cute that I've seen before include "Attractive and quaint (4" , "Small, delightful" , "Astute - lovely" , "Clever - attractive" , "Delightfully pretty or dainty" .)