Salesman, hero of American literature, not entirely austere (8)
I believe the answer is:
huckster
'salesman' is the definition.
(I've seen this before)
'hero of american literature not entirely austere' is the wordplay.
'hero of american literature' becomes 'huck' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'not entirely' means to remove the last letter (most but not all of the word).
'austere' becomes 'stern' (synonyms).
'stern' with its last letter taken away is 'ster'.
'huck'+'ster'='HUCKSTER'
Can you help me to learn more?
(Other definitions for huckster that I've seen before include "Aggressive salesman or hawker" , "bargain" , "Dodgy trader" , "Person using aggressive selling methods" , "Aggressive pedlar" .)