The word 'untrimmed' is a straightforward English formation built upon the verb 'trim'. The root 'trim' itself evolved from Old English trymman, meaning "to strengthen or make firm," which later specialized into the sense of preparing or arranging a ship's sails and, by the 16th century, took on the general meaning of cutting something to make it neat. The Old English negative prefix un- is one of the most common and persistent in the language, directly attached to the past participle form 'trimmed' to create an adjective describing something that has not undergone this process of cutting or tidying. Thus, the modern meaning logically follows from its components: the state of not having been cut or neatened.

Structure: un (not) + trim (cut) + ed (adjective suffix) - un: A prefix of Germanic origin (Old English un-) meaning "not," serving a negating function. - trim: A verb of Middle English origin (from Old English trymman, trymian meaning "to strengthen, arrange"), serving as the core root meaning "to cut or make neat." - ed: A suffix of Old English origin (-ed, -od), used to form adjectives from verbs, indicating the state or result of the action.