Step 1: Recall the definition. A synonym is a word that has the same or similar meaning as another word. Step 2: Test each option. 'Sad' = feeling unhappy → opposite of happy (antonym, not synonym). 'Glad' = feeling pleased or happy → same meaning as happy (synonym). 'Angry' = feeling annoyed or upset → different meaning. 'Tired' = feeling sleepy or exhausted → different meaning. Step 3: Select the answer. 'Glad' shares the same meaning as 'happy'. Answer: glad