A European could be big and lean (7)
I believe the answer is:
belgian
'a european' is the definition.
(Belgium is in Europe)
'could be big and lean' is the wordplay.
'could be' is an anagram indicator.
'and' means one lot of letters go next to another.
'big' put after 'lean' is 'leanbig'.
'leanbig' with letters rearranged gives 'BELGIAN'.
(Other definitions for belgian that I've seen before include "Bengali from a European state?" , "Hercule Poirot's nationality" , "Nationality of Rene Magritte" , "One from Liege, say" , "Eg, Brussels native" .)