Agent almost penniless (5)
I believe the answer is:
broke
'penniless' is the definition.
(thesaurus)
'agent almost' is the wordplay.
'agent' becomes 'broker' ('broker' can be a synonym of 'agent').
'almost' means to remove the last letter (most of the word but not all of it).
'broker' with its last letter taken away is 'BROKE'.
(Other definitions for broke that I've seen before include "Smashed; penniless" , "Bust - something to go for?" , "With completely empty pockets" , "Completely out of money" , "Shattered" .)