I could look up the definition of "Mammal"; it wouldn't include an expression of how to calculate anything.

Definitions don't need to do that.

On the contrary. A definition is exactly what tells you what the value of a quantity is.

Work is done when a force F moves through a distance D. E=Fd

If you add

F=MA

then you can calculate the KE of a body by calculating the work done by bringing it to a halt.

You can't do that if you have not yet defined energy. In this case the energy is energy of motion. What you've done is to take another quantity, the value of the work done, and called it "kinetic energy". If all we've done so far is to define "energy" then its premature to define "kinetic energy". One can easily define the term "kinetic energy" and calculate it as th work done in bringing a body of mass m from speed 0 to speed v. However that does not tell you what energy is. I.e. we have no idea yet of whether energy = kinetic energy.

If I were to define the term "energy" then I'd say that it's the sum of all the forms on energy such that the sum is an integral of motion (i.e. a constant of motion) for a closed system. Then we'd have to take care to find all those forms and then prove its such an integral. The problem is then reduced to finding all the forms of energy for a system. But to do that in general is not obvious and there is no general way to find all such quantities. I believe that's why Feynman said what he did.

Please answer my question, when does my definition fail?

I already did.

No, you didn't; the closest you got to doing so was to say "someone else says it doesn't- here's a reference which isn't readily available.

Your interpretation of the word "definition" means that you can't define anything that isn't described by an equation.

Since practically all the equations we see are approximations, that means you can't define anything.

A bit pointless really.

I have no problem with dealing with gravitational energy, nor with that associated with a point in an electrostatic field. It's the work done by a unit mass or charge "falling" from infinity to that point.

That's a force times a distance (albeit integrated because the force isn't constant).

So, yet again I'm asking where the definition fails.

Here's another way of looking at it.

There is a lot of cobblers talked about "energy" stuff about yin and yang; auoras and other dross.

A way to address that would be to replace the word energy in all science books with "Tctdw" (the capacity to do work).

In what branch of science would that not work?

I nearly forgot in all the excitement.

Feynman's point was, I believe, more or less the opposite of what you are saying.

His point was that, while we have lots of clever equations that let us calculate the paths of electrons or the speed of light, we don't really know what an electron or light actually are.

At that level it is perfectly true that we don't know what energy is; we just use t as an accounting tool- it lets us do clever things like pay the electricity bill, flatten a city or fly to the moon. But we still don't really know why.

Incidentally, since you still don't seem to get it, the capacity of a moving rock to do work is twice the capacity to do work of a rock (of the same mass) with twice as much energy. Such a pair of rocks can be shown by calculus to have velocities in the ratio 1 to √2.

A rock with twice the velocity can do 4 times as much work (if brought to a halt) and therefore has 4 times the energy.

That's why your assertion about e=mv is wrong; it gives the wrong answer.

As I recall, he likened it to a group of people looking at a bird; they can all give you the name of the bird in their various languages; but that tells you precisely nothing about the nature of the bird.