In Crete emeralds abound (4)
I believe the answer is:
teem
'abound' is the definition.
(I've seen this before)
'in crete emeralds' is the wordplay.
'in' indicates a hidden word.
'TEEM' can be found hidden inside 'crete emeralds'.
(Other definitions for teem that I've seen before include "Seethe" , "Pullulate" , "Come down hard" , "stream" , "pelt" .)