A keethera

The Keethera was, as approximately translated from Vulcan, a "structure of harmony." Constructing a keethera was a Vulcan meditation technique requiring precise balance and spatial acuity. It helped to focus thought and refine mental control. The structure, involving a group of building blocks, was different each time and dependent on the state of mind of the builder.

The following meditation was recited during the building of a keethera: "Structure. Logic. Function. Control. The structure cannot stand without a foundation. Logic is the foundation of function. Function is the essence of control. I am in control. I am in control." (VOY: "Flashback")

In the script pronunciation guide for "Flashback", the name of this type of structure was phonetically notated, "key-THER-uh".
The Star Trek Encyclopedia (4th ed., vol. 1, p. 408) spelled it Keethara.