What does add mean?
The definition of add
Add, v. t.
[imp. & p. p. Added; p. pr. & vb. n. Adding.] Etym: [L. addere; ad + dare to give, put. Cf. Date, Do.]

1 To give by way of increased possession (to any one); to bestow (on). The Lord shall add to me another son. Gen. xxx. 24.
2 To join or unite, as one thing to another, or as several particulars, so as to increase the number, augment the quantity, enlarge the magnitude, or so as to form into one aggregate. Hence: To sum up; to put together mentally; as, to add numbers; to add up a column. Back to thy punishment, False fugitive, and to thy speed add wings. Milton. As easily as he can add together the ideas of two days or two years. Locke.
3 To append, as a statement; to say further. He added that he would willingly consent to the entire abolition of the tax. Macaulay.

Synonyms
— To Add, Join, Annex, Unite, Coalesce. We add by bringing things together so as to form a whole. We join by putting one thing to another in close or continuos connection. We annex by attaching some adjunct to a larger body. We unite by bringing things together so that their parts adhere or intermingle. Things coalesce by coming together or mingling so as to form one organization. To add quantities; to join houses; to annex territory; to unite kingdoms; to make parties coalesce.

Add, v. i.
1 To make an addition. To add to, to augment; to increase; as, it adds to our anxiety. “I will add to your yoke.” 1 Kings xii. 14.
2 To perform the arithmetical operation of addition; as, he adds rapidly.