Add, the most general of these words, means to join one thing to another thing or to a group, series, or combination of other things so as to increase the original unit in numbers, size, amount
- added ten books to the library
- a little gossip adds spice to the conversation
- police action would add nothing to the protection that victims of aggression have enjoyed under the old system
One appends when one adds something that is supplemental and accessory and does not form an integral part of the principal thing.
- append notes to a book
- the final summary of his views which he enjoyed appending to his long-winded discourses
—I. V. Morris
One annexes when one adds something that becomes part of the original whole yet bears usually a subordinate or subsidiary relation to it or suffers loss of identity in the merging.
- annex a codicil to a will
- annex conquered territory to the kingdom
One subjoins when one adds something under another thing or especially to what has already been said or written.
- subjoin a postscript to a letter
- subjoin additional matter in an appendix
One superadds when one adds something to what is complete in itself or already at its maximum.
- the phrase “to paint the lily” means to superadd decoration to that which in itself is highly decorative
- the horrors of pestilence superadded to the horrors of war