The best word in the (English-speaking) world is field.
It's not diphthong. That's just juvenile. A word has to do more than sound funny to be the best word in the world.
Field does more than just about any word in existence, and everything it does is beautiful.
Field is a real, English word. It's very old. Along the way, it has fielded a vast field of meaning, if you will.
Field is one of the best nouns there is. It means, in its broadest sense, a thing-space: a space defined by the things in it.
We all know a field is an open plain or a meadow. That's one of the most beautiful kinds of field.
In fact, any kind of vast expanse, even of barren ice, is also a field.
We also know a field is a plot of land on which you grow a crop.
You also find natural resources like oil in a field.
But fields come even more basic than all that.
There's a mathematical definition of field, which I can't understand because I'm a word person, but I'm sure it's great.
“As an algebraic structure, every field is a ring, but not every ring is a field.”
It's a physics word meaning the area of space characterized by defined values of a physical property: a magnetic field, a gravitational field.
The area in which an optical lens renders an image is also a field.
There are multiple kinds of fields in computer science. A field is a defined area of an information storage medium, it's an element of a database containing a given piece of information, and it's an interface element like the one into which I'm typing right now.
Ah, but a field is also a place of work, both literally and figuratively. Sports are played on a field. War is waged on a field. Aircraft take off and land from a field. Even your area of work, your profession or discipline, is a field.
A field is so many more things, too. Because a field, at its essence, is a thing-space, a container for anything.
Field is a word so vast that to even define or enter a field creates a verb: to field! You field a ball, you field a candidate, you field an army, you even field questions!
And as if that wasn't enough, the word field is beautiful. It's a full, long syllable, wide enough in the mouth to be a field of its own.
Yes, English is a wide field. It has fielded an impressive field of entrants. But field is the most beautiful word in the world.