Can I write something once and use it in multiple topics?

Hello, I'm new to RoboHelp, and am wondering if this is possible... I have a bunch of topics where I list all the elements needed for XML messages 9one message per topic). Many of these elements (with their definitions) are used in many of the messages. This means that the same definition is shown in multiple topics. I would like to write each definition once, and and then shown wherever it's needed.

Also, many of the definitions include bullet lists, which I would like to show in two columns. I'm currently using tables to do this, but would prefer a better solution.

This is a new project, but I would like to incorporate it into our existing WebHelp system. But if there is a different output that would work better, we can consider that (though it would likely need to be a single file that we share with our customers).

Any help is greatly appreciated!!!