Periaktoi vs. Periaktos: What's the Difference?

Plural of periaktos

(historical) A revolving structure used to change scenes rapidly in a theatre: a tall prism-shaped frame or screen at the side entrances, each carrying a number of scenes changed by turning the frames.

A device for changing scenery in a theatre. A row of adjacent, three-sided columns form a backdrop to the stage and are turned in unison to show a different face.