Sincere answer Hemingway accepts? (7)
I believe the answer is:
earnest
'sincere' is the definition.
(synonyms)
'answer hemingway accepts?' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'hemingway' becomes 'ernest' (synonyms).
'accepts?' indicates putting letters inside.
'a' going within 'ernest' is 'EARNEST'.
(Other definitions for earnest that I've seen before include "showing seriousness" , "Eastern (anag.)" , "Something of value to bind a contract" , "Showing sincere and intense conviction" , "promise" .)