The word 'ungentlemanly' is a modern English formation built upon the well-established noun 'gentleman,' which itself has a rich history. 'Gentleman' originated in Middle English from gentil (meaning noble, kind, from Old French, ultimately from Latin gentilis 'of the same clan') combined with 'man.' The negative prefix 'un-', a direct descendant from Old English, is one of the most productive and ancient means of forming opposites in the language. Finally, the adjectival suffix '-ly,' also from Old English, is attached to convert the noun into a quality-describing adjective. Thus, the term's logic is transparently constructed: it literally describes the quality of 'not having the qualities of a gentleman,' directly reflecting its modern meaning of behavior contrary to accepted standards of male politeness and honor.

Structure: un (not) + gentleman (a courteous man) + ly (adjective suffix) - un: A prefix of Germanic origin (Old English un-), meaning "not." It functions as a negative particle. - gentleman: A noun of English origin, from Middle English gentilman, combining gentil (noble, courteous) and man. It functions as the core semantic base. - ly: A suffix of Germanic origin (Old English -līc), used to form adjectives meaning "having the qualities of." It functions as an adjectival suffix.