Dawn's answer spoken after posh reader's introduction (7)
I believe the answer is:
auroral
'dawn's' is the definition.
(I know this)
'answer spoken after posh reader's introduction' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'spoken' becomes 'oral' (similar in meaning).
'after' is a charade indicator (letters next to each other).
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'introduction' suggests taking the first letters.
The first letter of 'readers' is 'r'.
'u'+'r'='ur'
'oral' after 'ur' is 'uroral'.
'a'+'uroral'='AURORAL'
(Other definitions for auroral that I've seen before include "very early in the morning" , "Dawn's" , "Of the northern lights" .)