Adduction: Use the root "add" in the word.
Think of it as *adding* your arms to your body by pulling them *in* toward your center. For simplicity, I always gesticulate with my arms when I’m defining the word (even during a test in class). You should physically do this @Fiesty — I promise, it will help you remember.
Abduction: To abduct. To take something away. When you move your arms *out,* away from your body, you’re “abducting.”
Sorry, I don’t know a mnemonic, but I hope this helps!