Big mule loose in the country (7)
I believe the answer is:
belgium
'the country' is the definition.
(Belgium is an example)
'big mule loose' is the wordplay.
'loose' indicates anagramming the letters (letters are loosened from their original positions).
'big'+'mule'='bigmule'
'bigmule' is an anagram of 'BELGIUM'.
'in' acts as a link.
(Other definitions for belgium that I've seen before include "Country of Europe" , "Glib emu to be found in the country" , "Country north of France" , "Home of EU headquarters" , "One of the Low Countries" .)