largest
Biggest in size, amount, or degree in a group.
Largest means the biggest in size, amount, or degree when comparing three or more things. If you line up all the planets in our solar system, Jupiter is the largest because it's bigger than all the others. If you're comparing just two items, you'd say “larger,” but when there are three or more, the biggest one is the largest.
The word works for physical size (the largest building in town), numbers (the largest crowd ever recorded), or abstract measures (the largest contribution to science). When scientists talk about the largest animal that ever lived, they mean the blue whale, which can weigh as much as 200 tons and grow longer than three school buses parked end to end.
People sometimes confuse largest with most, but they measure different things. The largest country by area is Russia, but the country with the most people is India. You can have the largest slice of cake at the party but still not be the person who ate the most cake overall.