As yet wearing only underclothes, dress (6)
I believe the answer is:
invest
'as yet wearing only underclothes dress' is the definition.
'invest' can be an answer for 'dress' (thesaurus). I am not certain of the 'as yet wearing only underclothes' bit.
'underclothes dress' is the wordplay.
'underclothes' becomes 'in' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'dress' becomes 'vest' (vesting is a kind of dressing).
'in'+'vest'='INVEST'
Can you help me to learn more?
(Other definitions for invest that I've seen before include "Put money into shares, property, etc" , "Play the market" , "Lay out in expectation of profit" , "Buy shares; besiege" , "Eg, buy stocks and shares" .)