Pay attention and accept a flat, say (4,4)
I believe the answer is:
take note
'pay attention' is the definition.
(I've seen this before)
'accept a flat say' is the wordplay.
'accept' becomes 'take' (to accept is to take possession of).
'a flat say' becomes 'note' (A flat is a musical note).
'take'+'note'='TAKE NOTE'
'and' acts as a link.
(Other definitions for take note that I've seen before include "what the stenographer does" , "Observe closely" , "Pay attention" , "Observe and absorb - jot it down" , "mark?" .)