Related Clues:

• Put on halfway through first millennium in Rome?
• Tot; append
• Tot up
• Subtract's opposite
• Hit the plus button
• Stir in, say
• Make sense (with "up")
• Do a grade-school lesson
• Postfix
• Say also
• Calculate, in a way
• Do a grade school assignment
• Find sums
• Put (numbers) together
• Extend one's fingers, maybe