Vagrant losing millions in trick (4)
I believe the answer is:
trap
'trick' is the definition.
(I've seen this before)
'vagrant losing millions' is the wordplay.
'vagrant' becomes 'tramp' (I've seen this in another clue).
'losing' suggests deleting specific letters.
'millions' becomes 'm' (abbreviation).
'tramp' with 'm' taken away is 'TRAP'.
'in' acts as a link.
(Other definitions for trap that I've seen before include "It commonly has a role in speaking" , "Light carriage - it's sometimes sprung!" , "Ambush" , "Driver's obstacle" , "The Web" .)