Liberal Unionist saying nothing about private secretary payment (4,3)
I believe the answer is:
lump sum
'payment' is the definition.
(I know that lump sum is a type of payment)
'liberal unionist saying nothing about private secretary' is the wordplay.
'liberal' becomes 'l' (abbreviation).
'unionist' becomes 'u' (abbreviation as in Democratic Unionist Party).
'saying nothing' becomes 'mum' (I've seen this in another clue).
'about' is an insertion indicator.
'private secretary' becomes 'ps' (eg in PPS - parliamentary private secretary).
'mum' going around 'ps' is 'mpsum'.
'l'+'u'+'mpsum'='LUMP SUM'
(Other definitions for lump sum that I've seen before include "cash payout" , "Single cash payment" , "11 [LOLLY] as single amount" , "chunk of bread?" , "Single amount of money" .)