Meaning of addition reaction

addi'tion reac"tion

Pronunciation: [key]
— Chem. Chem.
  1. a reaction in which part of a compound is added to one end of a double or triple bond, while the rest adds to the other end, converting it, respectively, to a single or double bond.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.