Salty and blue novel about Oscar of course (10)
I believe the answer is:
absolutely
'of course' is the definition.
(thesaurus)
'salty and blue novel about oscar' is the wordplay.
'and' is a charade indicator (letters next to each other).
'novel' is an anagram indicator (letters in a new or novel order).
'about' is an insertion indicator.
'oscar' becomes 'O' (phonetic alphabet: alpha, bravo, charlie etc.).
'salty' put after 'blue' is 'bluesalty'.
'bluesalty' anagrammed gives 'abslutely'.
'abslutely' going around 'o' is 'ABSOLUTELY'.
(Other definitions for absolutely that I've seen before include "You bet!" , "Yes, indeed!" , "Dead" , "Utterly" , "I wholly agree!" .)