Prefix with chamber
I believe the answer is:
ante
'prefix with chamber' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ante that I've seen before include "A neat sort of prefix" , "Stake; before (Lat.)" , "Poker-player's stake before the deal" , "Stake (that may be upped?)" , "Money for poker" .)