The antonym for the word "un-tiring" is "tiring." This means that something or someone is causing fatigue or exhaustion. Synonyms for the word "tiring" include exhausting, strenuous, and draining. When something is tiring, it requires physical or mental effort that may lead to weariness. This can happen when engaging in manual labor or when dealing with a difficult task or circumstance. In contrast, when something is un-tiring, it does not cause fatigue or exhaustion, making it a more desirable option. Therefore, understanding antonyms can help us choose the most appropriate word in various situations.