Google is testing the ability to click on a word in a featured snippet within Google Search and define that word. You can also copy the word, if you want. I think this is a Google Search test and maybe not a Chrome test.

This was spotted by Punit who posted a video of this in action on Twitter, here is a screenshot of this video:

Here is the video embed:

Google added “define” option to know definition of selected Term (popup)
CC: @rustybrick pic.twitter.com/X2ungN8EeW

— Punit (@Punit6008) May 30, 2023

The reason I think this is a Google Search test and not a Chrome test is because he lost his Google session and was not able to trigger it again. I can be wrong and this might be a Chrome test and not a Google Search test.

Google is also testing this in other areas of the search results:

Google SERP is testing define options for the definition of limited search terms. Define options are shown in featured snippets, people also ask, Sponsored ads, organic results description & Local business. Have you seen this.

cc- @rustybrick @JohnMu

For referance video- pic.twitter.com/4mKuZ7csRa

— Anuj thaker (@Anuj_Thaker03) May 31, 2023

🧵 cc- @rustybrick pic.twitter.com/RRsLsbgVhJ

— Khushal Bherwani (@b4k_khushal) June 1, 2023

Here Sharing with you some example including wikipedia pages, I doubt for chroma features, asking for Ctrl+Shift+X for select pic.twitter.com/JOx9DhLoJF

— Punit (@Punit6008) June 1, 2023

Forum discussion at Twitter.