Dismiss from post (4,3)
I believe the answer is:
send off
'post' is the definition.
(thesaurus)
'dismiss from' is the wordplay.
'dismiss' becomes 'send' (I've seen this in another clue).
'from' becomes 'off' (eg someone might be from or 'off' a TV show).
'send'+'off'='SEND-OFF'
(Other definitions for send off that I've seen before include "Valediction" , "farewell party" , "Gathering for departure" , "dispatch" , "Order player to leave" .)