A2 to put two or more numbers or amounts together to get a total: If you add (= calculate the total of) three and four you get seven. It's $45 - $50 if you add in (= include) the cost of postage. Don't forget to add on your travelling expenses/add your expenses on.Augmenting and supplementing A2 to put something with something else to increase the number or amount or to improve the whole: Beat the butter and sugar together and slowly add the eggs. She's added a Picasso to her collection. Her colleagues' laughter only added to (= increased) her embarrassment.Augmenting and supplementing B1 to say another thing: [+ that] She was sad, she said, but added (= said also) that she felt she had made the right decision. [+ speech] "Oh, and thank you for all your help!" he added as he was leaving.