The many and varied definitions of set mean that it takes up more space in the dictionary than any other word.

There is a Fuegian word that used to be classed as the most succinct. The (rough spelled!) word is mahmalapinatapai, and it means something like the state of two or more persons, who are looking at each other in the hope that one of the the others will do something that both parties desire but that neither is willing to do themselves.

How about: color or shape?

color: a visual attribute of things that results from the light they emit or transmit or reflect; "a white color is made up of many different wavelengths of light

"is" is a verb

a particular color would be kind of hard to define, like green
I guess

colors only have ostensive definitions, as do directions like left (i.e., you can only define it by pointing). you can make a verbal definition but it will generally be at least somewhat circular.

as for the definition of "is," that depends on what you mean by "is." (not to wax clintonian.) there's the is of identity (e.g., water is h20), the is of existence (e.g., there is a computer in this room), the is of predication (e.g., this shirt is black), the is of identification (e.g., this is a cup), the is of artistic identification (provided you're arthur danto . . . e.g., this white dot in the painting is icarus) . . .

is - pertaining to

Is is the present form of "to be" for he/she/it. If I was teaching the English language, that's how it would be.