The antonym for tired is "energetic". To find the antonym of a word, you can use a thesaurus. A thesaurus is a reference book that provides synonyms (words with similar meanings) and antonyms (words with opposite meanings) for various words. You can find a thesaurus online or use a physical thesaurus. In this case, you can look up the word "tired" in the thesaurus and find its antonym, which is "energetic".