Son biting Dawn? (5)
I believe the answer is:
start
'dawn?' is the definition.
(dawning is a kind of starting)
'son biting' is the wordplay.
'son' becomes 's'.
'biting' becomes 'tart' (I've seen this before).
's'+'tart'='START'
(Other definitions for start that I've seen before include "begin an argument?" , "Take the first step" , "Beginning" , "Begin - opening move" , "Jump suddenly" .)