Lay out wearing undergarment? (6)
I believe the answer is:
invest
'lay out' is the definition.
(to lay out is to invest money)
'wearing undergarment' is the wordplay.
'wearing' becomes 'in' (you are 'in' the clothes you're wearing).
'undergarment' becomes 'vest' (vest is a kind of undergarment).
'in'+'vest'='INVEST'
(Other definitions for invest that I've seen before include "Put money into in hopes of a return" , "Place money in a scheme" , "Eg, buy stocks and shares" , "Put money into business for profit" , "as Greeks did to Troy?" .)