an upright frame or tripod to hold an artist's canvas, a picture on display, etc.
See easel in American Heritage Dictionary 4
(ēˈzəl)
noun
An upright frame for displaying or supporting something, such as an artist's canvas.
Word History: “A painter's ass” is not a phrase that immediately brings to mind an accessory to the artist's profession. But easel comes to us from the Dutch word ezel, meaning “ass, donkey.” The Dutch word was eventually extended to mean “an upright frame for displaying or supporting something,” in the same way that the English word horse has come to mean “a piece of gymnastic equipment with an upholstered body.” Developments such as these illustrate the playfulness or wit that speakers often bring to language, here applying the name for one object to another with similar properties.