Hi there,
I would recommend you to "use the search the web for..." feature to find the definition of the word/phrase which you can use by right-clicking the selected phrase and use the "use the search the web for..." option. You can also use the upcoming sidebar search feature which will search it in a bar on the right without opening a new tab to find the definition easily (Note: The sidebar search feature is still not yet available for the stable channel and will be coming in the few months.)
Lastly, if you want to use a third-party extension to see the meanings, I would recommend you the Grammarly extension which has this optional feature where you can double-click a word and find the meaning easily in a popup for that word