American opportunely heads for high yields, displaying coolness (6)
I believe the answer is:
apathy
'coolness' is the definition.
(I've seen this in another clue)
'american opportunely heads for high yields' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'opportunely' becomes 'pat' (pat can mean conveniently or opportunely).
'heads for' indicates taking the first letters.
The initial letters of 'high yields' is 'hy'.
'a'+'pat'+'hy'='APATHY'
'displaying' is the link.
(Other definitions for apathy that I've seen before include "Absense of interest or emotion" , "Unconcern" , "Absence of emotion or enthusiasm" , "Absence of interest or emotion" , "Lack of excitement" .)