《礼记·郊特牲》
加冠时给冠者取一个字，从此以后就要以字相称而避讳其名，这表示对父母所取之名的敬重。
冠而字之，敬其名也。委貌，周道也。
When adding a crown, a word is given to the crown wearer, and from then on, he will be called by his word and avoid his name, which shows respect for the name given by his parents.