ftak

ftak is a free Chrome extension for looking things up without leaving the page. Double-click or drag over a word or phrase and a small tooltip shows its meaning, a short summary from Wikipedia, and a map if it is a place. Click away and you are back to reading.

No tab switching, no copy-paste, and no sign-up. There is also a PDF reader on the site where you can look up words inside a PDF the same way.

UPSC aspirants can also see related previous-year UPSC questions for text they select in news articles (a few free each day, more after signing in).