Posts include gratuity and wages (8)
I believe the answer is:
stipends
'wages' is the definition.
(I've seen this in another clue)
'posts include gratuity' is the wordplay.
'posts' becomes 'sends' ('send' can be a synonym of 'post').
'include' indicates putting letters inside.
'gratuity' becomes 'tip' (as in a gratuity to a waiter).
'sends' placed around 'tip' is 'STIPENDS'.
'and' is the link.
(Other definitions for stipends that I've seen before include "Salaries of clergymen" , "Allowances (clergy)" , "Spends it on clergymen's salaries" , "Official incomes of clergymen" , "Regular payments" .)