《论衡·卷一·气寿篇》
比如人的身高一丈，是正常形体。所以称男子为丈夫，尊称老头，老妇为丈人。
譬犹人形一丈，正形也，名男子为丈夫，尊公妪为丈人。
For example, a person's height of one zhang is a normal figure. Therefore, a man is called a husband, and an old man and an old woman are called zhangren.