The word 'undefended' is a straightforward English formation built upon the core verb 'defend.' The verb itself entered Middle English from Old French defendre, which descended from Latin dēfendere, meaning "to ward off, strike away, protect." The Latin term is a compound of dē- ("from, away") and -fendere (from the root gʷʰen-, "to strike, slay"), thus carrying the literal sense of "to strike away" a threat. The negative prefix un-, a common and ancient Germanic formative, was attached to the past participle 'defended' to create an adjective describing a state of being unprotected, either physically from assault or logically from criticism.

Structure: un (not) + defend (protect) + ed (adjective suffix) - un: A prefix of Germanic origin (Old English un-), meaning "not." It functions as a negative particle. - defend: A verb of Latin origin (dēfendere, "to ward off, protect"). It functions as the core lexical root. - ed: A suffix of Germanic origin (Old English -ed, -od), used to form adjectives from verbs, indicating a state or condition.