Campaign funds western, with most knowing to support it (3,5)
I believe the answer is:
war chest
'campaign funds' is the definition.
(I've seen this before)
'western with most knowing to support it' is the wordplay.
'western' becomes 'w'.
'with most knowing' becomes 'arches' (I can't explain this - if you can you should believe this answer much more).
'to support' says to put letters next to each other (in a down clue, some letters hold others up).
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'w'+'arches'+'t'='WAR-CHEST'
Can you help me to learn more?
(Other definitions for war chest that I've seen before include "hypothecated funds" , "funds for action?" , "Funds set aside" , "ready for fighting?" , "Fighting fund" .)