1 join, unite, combine, annex:
5 + 3 denotes that 3 is to be added to 5.
2 total, sum, sum up, combine, count up, reckon, Brit tot (up), US tote (up):
The computer can add all those figures in a few seconds.
3 continue, go on:
'And I won't take no for an answer', she added.
4 add to. increase, enlarge, amplify, augment, supplement:
His articles have added greatly to his reputation as a financial analyst.