英语词源字典 - 在线词源网站

underdressed (adj.)[underdressed 词源字典]: also under-dressed, "too plainly dressed," 1759, from under (adv.) + past participle of dress (v.).[underdressed etymology, underdressed origin, 英语词源]
undressed (adj.): "naked (or nearly so)," 1610s, past participle adjective from undress (v.).