While some people might use other terms like "fissure" or "crack", "joint" is the most precise and common geological term for a fracture in rock where there is no relative movement of the rock on either side of the fracture.

Here are some other terms that could describe a vertical gap in limestone, depending on the context:

* Fissure: This term is often used for a wider gap or crack, but it can also be used for a joint.

* Crevice: Similar to a fissure, this term is often used for a narrow, deep gap.

* Fault: This term describes a fracture in the rock where there has been movement along the fracture.

Ultimately, the best term to use will depend on the specific characteristics of the vertical gap in the limestone.