Practice to which America for example reverts (5)
I believe the answer is:
usage
'practice' is the definition.
(I know that usage is a type of practice)
'america for example reverts' is the wordplay.
'america' becomes 'usa' (United States of America).
'for example' becomes 'e.g.' (short for 'exempli gratia', 'for example' in Latin).
'reverts' says the letters should be written in reverse.
'eg' written backwards gives 'ge'.
'usa'+'ge'='USAGE'
'to which' is the link.
(Other definitions for usage that I've seen before include "Convention" , "Way of employing" , "Employment - practice" , "Silly little thing" , "Treatment; tradition" .)