The word 'undress' is a straightforward English formation, combining a native Germanic prefix with a verb of French-Latin descent. The prefix 'un-' acts as a reversative, signaling the removal or reversal of the action denoted by the base verb 'dress.' While 'dress' evolved from a Latin root meaning "to make straight or direct," its meaning specialized in Middle English to "to arrange, adorn, or put clothes on." Therefore, 'undress' logically means to reverse the act of putting on clothes. This transparent construction exemplifies how English frequently creates antonyms by attaching the productive prefix 'un-' to verbs of various origins.

Structure: un (reverse action) + dress (to clothe) - un: A prefix of Germanic origin (Old English un-, on-), meaning "to reverse, remove, or deprive of." It functions as a reversative or privative prefix. - dress: A verb from Old French drecier (to arrange, set right), ultimately from Latin directus (straight, direct). In this context, it carries the sense "to clothe or attire."