Salutation knocked back graduate, sad to say (6)
I believe the answer is:
salaam
'salutation' is the definition.
(salaam is an Arabic greeting or salutation)
'knocked back graduate sad to say' is the wordplay.
'knocked back' says the letters should be written in reverse.
'graduate' becomes 'MA' (abbreviation for Master of Arts).
'sad to say' becomes 'alas' ('alas' is said before reporting something sad).
'ma'+'alas'='maalas'
'maalas' reversed gives 'SALAAM'.
(Other definitions for salaam that I've seen before include "Muslim form of salutation" , "Oriental bow and salutation" , "Oriental salutation meaning peace" , "Oriental greeting like low bow" , "Muslim greeting gesture" .)