Related Clues:

• Desirable extra
• "Besides . . ."
• "Besides that ..."
• "Not only that . . ."
• 26-Across enhancement
• "Besides that . . ."
• Sign between numbers, sometimes
• Sign in addition problems
• Boon
• And, in addition?
• Addition word
• Together with
• A follower, sometimes
• Certain calculator symbol
• Perk