Lay out trendy American waistcoat (6)
I believe the answer is:
invest
'lay out' is the definition.
(I've seen this before)
'trendy american waistcoat' is the wordplay.
'trendy' becomes 'in'.
'american waistcoat' becomes 'vest' (US term for a waistcoat).
'in'+'vest'='INVEST'
(Other definitions for invest that I've seen before include "Put money into in hopes of a return" , "Put money into business for profit" , "Formally place in office" , "Contribute money in hopes of financial return" , "Place money in a scheme" .)