Say line at end of play? Absolutely! (7)
I believe the answer is:
utterly
'absolutely' is the definition.
('utterly' can be a synonym of 'absolutely')
'say line at end of play?' is the wordplay.
'say' becomes 'utter' (I've seen this before**).
'line' becomes 'l'.
'at end of' says to take the final letters.
The last letter of 'play' is 'y'.
'utter'+'l'+'y'='UTTERLY'
(Other definitions for utterly that I've seen before include "Completly and without qualification" , "In all respects" , "'All is changed, changed . . .' (Yeats)" , "unqualified" , "Completely and totally" .)