骑 (qí) — to ride (a horse, bike, or other vehicle one sits astride)

骑 (qí) is the verb for riding something you sit astride — a bike, horse, or motorcycle. 乘坐 is for vehicles you sit inside (bus, train, plane).

Most characters — around four in five — are built this way: one part hints at the meaning, the other at the pronunciation.

This origin belongs to the traditional form 騎; 骑 is its simplified writing.

The traditional form 騎 combines 馬, meaning horse, with 奇, which supplies the sound, for riding a horse; the simplified 骑 is a later shorthand.