The word 'untiring' is a straightforward English formation built upon the native Germanic verb 'tire,' which descends from the Old English tēorian, meaning "to fail, cease, become weary." This Old English term is of uncertain deeper origin but is part of the Germanic lexical family. The prefix 'un-', from Old English, is added to negate the root, creating the sense of "not becoming weary." The adjectival suffix '-ing,' also from Old English, transforms the verbal phrase into a descriptive quality. Thus, the literal construction "not-wearying" logically yields the modern abstract meaning of persistent and indefatigable effort.

Structure: un (not) + tire (exhaust) + ing (adjective suffix) - un: A prefix of Germanic origin (Old English) meaning "not," serving a negating function. - tire: A verb of Germanic origin (Old English tēorian, tȳrian) meaning to become weary or exhausted, serving as the core lexical root. - ing: A suffix of Germanic origin (Old English -ende, -inge) used to form present participles and adjectives, indicating a quality or state.