As yet wearing only underclothes, dress (6)
I believe the answer is:
invest
'dress' is the definition.
(thesaurus)
'as yet wearing only underclothes' is the wordplay.
'as' becomes 'in' (I've seen this in other clues).
'yet wearing only underclothes' becomes 'vest' (I can't justify this - if you can you should give a lot more credence to this answer).
'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" .)