Han character 驂

驂 names the auxiliary horses beside a chariot’s central pair. The Shuowen Jiezi, an early Chinese dictionary, describes a three-horse team; later explanations use 驂 for the outer horses in a four-horse team. The earliest surviving forms appear in Chu manuscripts written on bamboo slips and silk; later examples appear in small-seal and clerical script, two historical Chinese writing styles. The sequence shows a character that developed through successive forms.

In Classical Chinese, its sense broadened to “horse” generally and the verb “to ride or drive.” Japanese reference works also retain the auxiliary-horse sense and use 驂 for a companion riding beside a person of rank.

Someone sent me 驂—what should I read?

Treat it as a literary word; the surrounding text determines its sense. A bare 驂 could be an excerpt or a dictionary lookup. The neighboring words show whether it refers to the outer horses, a horse generally, or riding.