I wanted to think of a different target then those ideas floating out there already. I have many students that are starting to understand synonyms just are having difficulties with demonstrating this skill in a variety of ways. So I created a listening for synonyms activity with the popcorn theme. Students will pick a piece of popcorn then either read it themselves or hand it to me to be read to them. Students must identify the word in the sentence that has a synonym and verbally express it to the group. If correct, they can put the popcorn in their container. But watch out for the elephants! They LOVE popcorn! If they pick an elephant they must empty out their containers!! The student with the most popcorn at the end, wins!
You can review all the vocabulary/synonym pairs ahead of time to help them out if necessary. You can also display all the "other pairs" on a dry erase board or poster display to help with recall if necessary as well. You can also tell them which word to provide a synonym for if that's the level your students are.