Custom from America, say, taken up (5)
I believe the answer is:
usage
'custom' is the definition.
('usage' can be a synonym of 'custom')
'america say taken up' is the wordplay.
'america' becomes 'usa' ('U.S.A.' can be a synonym of 'america').
'say' becomes 'eg'.
'taken up' shows that the letters should be reversed in order.
'eg' backwards is 'ge'.
'usa'+'ge'='USAGE'
'from' acts as a link.
(Other definitions for usage that I've seen before include "Silly little thing" , "Convention" , "Acceptable language" , "Way of treating" , "Way of employing" .)