add / ad/ • v. [tr.] 1. join (something) to something else so as to increase the size, number, or amount: a new wing was added to the building [intr.] this development added to the problems facing the staff. ∎  [intr.] (add up) increase in amount, number, or degree: watch those air miles add up! ∎  put or mix (an ingredient) together with another as one of the stages in the preparation of a dish: add the flour to the eggs. ∎  put (something) in or on something else so as to improve or alter its quality or nature: chlorine is added to the water to kill bacteria. ∎  contribute (an enhancing quality) to something.2. put together (two or more numbers or amounts) to calculate their total value: they added all the figures up [intr.] children learned to add and subtract. ∎  [intr.] (add up to) amount to: this adds up to a total of 400 calories | fig. these isolated incidents don't add up to a true picture of the situation. ∎  [intr.] (add up) inf. seem reasonable or consistent; make sense: many things in her story didn't add up.3. say as a further remark: we would like to add our congratulations.

add unite, say in addition, perform the arithmetical process of addition. XIV. — L. addere, f. AD- + base of facere DO1.
So addendum, pl. -a XVIII. sb use of gerundive of L. addere, additament XIV. — L. additāmentum, f. addere, addit-. addition XIV. — F. or L. Hence additional XVII; cf. F. additionel. additive XVII. — late L. additīvus.

ADD • abbr. ∎  analog digital digital, indicating that a music recording was made in analog format before being mastered and stored digitally. ∎  attention deficit disorder.