Crazy about new American singer (7)
I believe the answer is:
madonna
'singer' is the definition.
(American singer)
'crazy about new american' is the wordplay.
'crazy' becomes 'mad' (synonyms).
'about' becomes 'on' (as in a book 'on' a certain topic).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'mad'+'on'+'n'+'a'='MADONNA'
(Other definitions for madonna that I've seen before include "Virgin Mary - or American showbiz queen" , "Like a Virgin singer" , "Religious work" , "Virgin Mary; singer" , "Religious art subject - pop singer, b. 1958" .)