the word 'tireless' is a relatively modern english formation, built from native germanic components. the root 'tire' descends from the old english verb 'teorian', which carried the sense of becoming weary or failing, a concept with deep germanic roots. this is combined with the prolific old english suffix '-lēas', meaning 'without' or 'free from', which is cognate with the modern german '-los'. the literal construction "without tiredness" logically yields the modern abstract meaning of showing inexhaustible energy and perseverance. it exemplifies how english can create potent descriptive terms by combining its ancient core vocabulary.

Structure: tire (exhaust) + less (without) tire (from old english 'teorian', meaning to become weary, fail, cease; of germanic origin, functioning as the verb root) + less (from old english '-lēas', meaning devoid of, free from; a suffix forming adjectives, of germanic origin)