add (v.) Look up add at Dictionary.com
late 14c., "to join or unite (something to something else)," from Latin addere "add to, join, attach, place upon," literal and figurative, from ad "to" (see ad-) + -dere, combining form meaning "to put, place," from dare "to give" (from PIE root *do- "to give"). Intransitive meaning "to do sums, do addition" also is from late 14c. Related: Added; adding. To add up is from 1754; in the figurative meaning "make sense," 1942. Adding machine "machine to cast up large sums" is from 1822.