Deploying thought after losing millions (5)
I believe the answer is:
using
'deploying' is the definition.
'thought after losing millions' is the wordplay.
'thought' becomes 'musing' (musing is a kind of thought).
'after losing' suggests deleting specific letters.
'millions' becomes 'm' (abbreviation).
'musing' with 'm' taken away is 'USING'.
(Other definitions for using that I've seen before include "Putting into service" , "Utilising" , "having recourse to" , "practice" , "Employing" .)