Glossary Definition Formatting: Storyline 360

The built-in Glossary doesn't provide formatting or linking options.

You could create a custom Glossary. Here's a post about how to create a custom tab in the Player. 

https://community.articulate.com/discussions/articulate-storyline/tip-create-custom-player-tabs-for-your-resources-glossary-and-more 

The post also includes a link to a sample Custom Glossary. I'm sure you can find other types if you search the Forum. 

Note: The main disadvantage of custom glossaries is sorting. You're responsible for ensuring they appear in alphabetical order. (Depending on how the glossary is set up, that could be especially tricky if the course is translated.)

Storyline supports a few (very limited) tags to format variables:

https://articulate.com/support/article/Storyline-360-Using-HTML-Formatting-Tags-in-Text-Variables

I tried these with a definition in the built-in glossary feature and they seem to work.

I tried a few other tags with glossary definitions that are not listed in the support article above and they seem to work as well, including:

underline (<u>...</u>)

strikethrough (<strike>...</strike>)

mark (or highlight) (<mark>...</mark>).