add

An act or instance of adding.

An additional enemy that joins a fight after the primary target.

"When the player has fought the boss for one minute, two adds will arrive from the back and must be dealt with."

To join or unite (e.g. one thing to another, or as several particulars) so as to increase the number, augment the quantity or enlarge the magnitude, or so as to form into one aggregate.

To sum up; to put together mentally.

"to add numbers"

To combine elements of (something) into one quantity.

"to add a column of numbers"