Either 2, in ''2+2''

• Quantity to be appended
• Either "2" in "2 + 2 = 4"
• Portion of a sum
• A number that is added to another number (the augend)
• Number in a sum
• Sum thing
• Part of the total
• Number on either side of a plus sign
• Math-sum unit

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
addend \addend\ n. 1. a number that is added to another number. [WordNet 1.5] ||