The definition of a matron of honor is a woman, often an older or married woman, who is chosen by the bride at a wedding to stand up for the bride and to be an assistant in the planning and carrying out of the wedding.(noun)
An example of a matron of honor is the older and married best friend of a bride who throws the bridal shower and who walks down the aisle right before the bride at the wedding.
See matron of honor in Webster's New World College Dictionary
See matron of honor in American Heritage Dictionary 4