Variant of 轂

It is a variant form of 轂, the center of a wheel. The Chinese word 轂 names the wooden hub where the spokes meet and the axle passes through. In standard Chinese writing, 轂 is the familiar form.

How did 轂 acquire a wider meaning?

The wheel part could stand for a whole carriage. The history of the standard character 轂 includes Chu and Qin bamboo writing; the Han dynasty dictionary Shuowen Jiezi defines it as the place where spokes gather. Classical texts also use it for a carriage, as in 朱輪華轂 (“a splendid carriage”).