PA's said why beforehand (6)
I believe the answer is:
yearly
'pa's' is the definition.
(abbreviation for 'per annum', meaning 'yearly')
'said why beforehand' is the wordplay.
'said' shows a homophone (sound like).
'beforehand' becomes 'early' ('early' can be similar in meaning to 'beforehand').
'why' is a homophone of 'y'.
'y'+'early'='YEARLY'
(Other definitions for yearly that I've seen before include "At annual intervals" , "Annually" , "Happening every twelve months" , "A hundred times a century" , "Unpleasant noise" .)