Deck idiot descending on ambassador (6)
I believe the answer is:
'deck' is the definition.
'idiot descending on ambassador' is the wordplay.
'idiot' becomes 'clot' (both can mean a stupid person).
'descending on' says to put letters next to each other (in a down clue, some letters go on top of others).
'ambassador' becomes 'HE' (His or Her Excellency).
(Other definitions for clothe that I've seen before include "Invest" , "Provide cover for body and limbs" , "Put garments onto" , "Equip" , "robe" .)