Some Common Market countries - and the rest (3)
I believe the answer is:
etc
'and the rest' is the definition.
(et cetera)
'some common market countries' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'ETC' is hidden in the letters of 'common market countries'.
(Other definitions for etc that I've seen before include "Etcetera (abbrev.)" , "And so on, in brief" , "'And the rest, in short (3)'" , "And so forth (abbr)" , "And so on, briefly" .)