Ranking synonyms of body shapes? underweight->overweight?

On the underweight list – I think you’re confusing the reason for the body condition with the condition itself.

For example – a bony person could be starved or malnourished.

@elbanditoroso has it right. If you don’t what contributed to their being underweight, I would use “thin” or “skinny.” “Bony” is more descriptive of a certain kind of underweight.

Any of the terms for overweight are possible but have different connotations. I might be described as “chubby’ or “pudgy” but I am not obese which means very overweight. Fat and corpulent are slightly more pejorative and “stout” is more of a stuffy old-fashioned term.

Keep in mind that terms like “thin” are also often subjective, so what is thin to some may be considered not so thin to others.

Welcome to Fluther! Good question!

@elbanditoroso is correct, in particular about these:

malnourished – this is about not getting the right nutrition
starved – this is about not getting nearly enough food
undernourished – this means getting less food than needed
bony – this is about visually noticeable bones, but isn’t really on a scale of overall thinness

stout – this means short but stocky. It’s not a degree of overweight.

The gradations don’t have a precise order or meaning in general English, but I would tend to think of the others arranged a bit like this:

heavy
pudgy
chubby
corpulent (this one isn’t necessarily on a scale with the others, though)
fat
obese (this one also has a medical definition that can technically apply to people who don’t look particularly healthy, depending on their body type)
morbidly obese

On the thin side:

thin
skinny
very skinny
skeletal (though this means you’re starting to look like a skeleton)

I don’t understand what you mean by putting them in order. They don’t have an exact value that would rank them from most to least.

For example, for “stout,” dictionary.com says: “bulky in figure; heavily built; corpulent; thickset; fat.” (@Zaku, I don’t think shortness is part of it at all. One could, for example, describe Donald Trump as “stout,” and it would be both accurate and less pejorative than “obese.” Whatever he is, he isn’t short.)

@Jeruba Oh, it appears you’re right. (I have a connotation of “stout” with “short”... maybe it goes back to “I’m a little teapot”.)