Google has added those definition-based contextual links to some of the words placed in the Search Generative Experience answers and results. This is very similar to the featured snippet injected definition links but in this case, you can trigger a conversation in SGE when you ask for more details.
Google said that they “will soon roll out improvements to our AI-generated responses for various topics or questions related to STEM, economics, history and more. With this update, you’ll be able to hover over certain words to preview definitions and see related diagrams or images on the topic.”
Here is a GIF of it in action (click to enlarge):
When you tap on the message on the bottom of the pop-up window that says “Tell me more about [topic],” it takes you to the Search Generative Experience conversation mode, where you’ll see more about the topic that’s referenced.
This is less problematic than the featured snippet injection of contextual links because at least with SGE it is using dozens of pieces of content to generate the text whereas with featured snippets it was using a singular source and then changing that content to add its own links. So this is less problematic.
Forum discussion at Twitter.