cool one's heels, to

Fig. to wait (for someone); to wait for something to happen. I spent an hour cooling my heels in the waiting room while the doctor saw other patients. All right, if you can't behave properly, just sit down here and cool your heels until I call you.

Wait or be kept waiting, as in I've been cooling my heels in the doctor's waiting room for at least an hour. This term originally meant to cool one's feet when they become hot from walking, and began to be used ironically for being forced to rest (or wait) in the early 1600s.

To wait or be kept waiting.

To be kept waiting. Presumably this saying comes from the fact that one’s feet become warm in the act of walking and cool off when one sits or stands still in the act of waiting. It dates from the early seventeenth century and was common enough by the 1630s to appear in several sources (William Rowley, Thomas Dekker). A century later, Henry Fielding wrote, “In this parlour Amelia cooled her heels, as the phrase is, near a quarter of an hour” (Amelia, 1752).