How would you describe "being something and not any other thing"? One thing can be many things to many people.
In the example from Geoffrey Thomas of cow and non-cow, there are many definitions on what that can mean. City dwellers will call anything "cow shaped" a cow, even though the word "cow" means a female bovine that has bred. Male bovine are bulls, and neutered male cattle are called steers.
Personally, I also call them steaks, burgers, and lots of other tasty food, as well as leather. Some people might define me as a cow, which would be someone who stuffs their face with food.
What do you call this?
Some people call them slotted screw drivers, while others call them flat bladed/head screw drivers. I call them small pry bars, box cutters, letter openers, chisels, a small hammer, an awl, hole finder, and even juggling prop, among many others.
Just because something is supposed to be one thing, it doesn't mean it can't be other things as well.
The chair you mentioned can be a short table, if you sit on the floor, or a foot stool. It can also be a door jamb, a shelf, foot rest, and has a host of other uses. Add a sheet and a small child's imagination, it can be a mountain or a tent.
I would think, due to the wide ranging use of items and the inaccurate descriptions that language tries applies to them, that to be "something and not any other thing" is next to impossible. Is there anything that can't be used for something other than it was intended for? Even a mind or talent can be used or wasted.
I would also think that having a definition is good enough for something to exist. We have definitions for things that we aren't sure physically exist (like unicorns and certain subatomic particles), but they at least exist in the imagination.
Being human isn't just one thing. Being human means being lots of things.
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects. - Robert A. Heinlein
I should also explicitly mention that the "thing that is defined" can be redefined as time goes on. A cow was once "something else" in that it had to be a heifer (unbred female bovine) before it could be a cow. A steer was a bull, until it is castrated.
Even a small pry bar was a screw driver, until I use it to open a can of paint, then it turns into a stir stick, then a hammer (to put the lid back on), and finally turns back into a screw driver when it returns to my toolbox. According to someone else's philosophy, I should be using different tools for each step. I actually have a paint can opener, many wooden stir sticks, and a couple of hammers, but why go find them when I have my all-in-one tool? Sure, the real stir stick does a better job, and I might usually use one, but maybe I just need to check if the paint is still good.
Language is used as a way to describe what we perceive and what we perceive can become knowledge. Philosophy is defined as "the study of the fundamental nature of knowledge, reality, and existence", so a case can be made that philosophy is a study of the descriptions of how people perceive knowledge, reality, and existence.
Two people can witness the same thing, but from different perspectives, and gain different knowledge. For instance, one witness of a stabbing might "learn" to not trust people of a certain skin color, while another might "learn" not to go to that part of town after dark, while yet another might "learn" not to shout profanity at someone who has with a knife. Get these three people in the same room, and they will use language to try to convince the others of how correct their knowledge is.
If I tell you that the little gooey spots on the bottom of your mouse and attached to your mouse pad is actually dead skin cells and oils from your hand, as it rubs against the surfaces of the table and mouse, isn't that going to change your philosophy on hygiene at your computer desk? I likely just used language to cause you to cringe away from your mouse, maybe grab some Lysol, and possibly even to never eat at your desk again.
But does usage define the item or the item define usage? A screw driver was made for a specific use, hence the name and definition, but I'm redefining by my usage. It didn't go through any metamorphosis while I was using, it was still the same thing I pulled out of my toolbox.