Alonzo, you seem to have a poor grasp of the principles of rational argument.
First, I have enough of a grasp of the principles of rational argument to recognize a distinction between attacking an argument and attacking a person.
Second, I also have sufficient grasp of the principles of rational argument to recognize that "complex question" is listed as a fallacy. Assuming that one has never beaten one's wife, the answer to the question, "Do you still beat your wife?" is neither "yes" nor "no" no matter how many times a person insists on a "yes" or "no" answer.
"Ought" refers to reasons for action that exist. If you tell me that I ought to do something, and I ask "Why?", then the only sensible response is to give me a reason for action that exists. If it is not a reason for action, then it is irrelevant to the question of what I ought to do. If the reason for action does not exist (is fictitious), then the conclusion is grounded on a false premise.
Your standard for a definition - a word or phrase that can be substituted for another word or phrase without changing the meaning - is flawed. Very few words can be defined that way. If you think you can do it, then give me a definition for life? species? love? game? food? house? law?
Also, answer for me the question of how the first word was defined? It certainly was not defined by a caveman who said, "By rock, you are to understand me to mean the following...."
Our language is filled with vague and ambiguous words.
This is because language is a tool. It takes energy to prefect a language, so we tend to design our language - like we design any tool - to be "good enough" to do the job we need to have done.
"Ought" is one of those terms that, in English, is both vague and amiguous. As such, a "perfect" descriptive definition (a definition that describes how the word is used) would have to be equally vague and ambiguious. Which is not what I am after. Talk to a sociologist if you want that type of definition. I am not interested in a descriptive definition but a prescriptive definition - an account not of how the word is used, but of how the word should be used.
Recently, you made comments that suggested that "approval" or "disapproval" is a part of the definition of moral "ought".
This is false.
It may be the case that people only truthfully assert, "X is immoral" if they disapprove of X. However, this does not imply that it is a part of the meaning. After all, people only truthfully assert, "X is true" if they believe that X is true. However, their belief is not a part of the meaning.
That is to say, they do not infer that if they did not believe that X would true then by definition X would no longer be true.
If approval or disapproval was a part of the meaning of moral terms, then moral debate would not make sense. Moral debate lives on the assumption that X can be wrong even though the speaker does not disapprove of it, or not be wrong even though the speaker does disapprove of it.
Person 1: Abortion is not wrong.
Person 2: You are mistaken. Abortion is murder.
Person 1: I cannot be mistaken. "Abortion is wrong" means "I do not approve of abortion". Since it is not the case that I do not approve of abortion, it is not the case that abortion is wrong. If you wish to convince me that abortion is wrong, then, by definition, you must convince me that I do not approve of abortion."
Moral debates are not debates about what people do or do not approve of. Moral debates are debates about what people should or should not approve of. To answer these questions, the disputants look for "reasons for action that exist" for approving or disapproving of abortion.
Note, here, that there is a difference between reasons for action that exist for having or not having an abortion and reasons for action that exist for approving or disapproving of abortion. One of the reasons one can give against committing rape is that it is immoral.
To say that rape is immoral is not to say that we do not approve of rape, but that we should not approve of rape. Applying the above definition of "ought" to the question of approving of rape, we see that moral questions are primarily about reasons for action that exist for promoting disapproval of rape.
The idea that moral questions are primarily about actions is a common mistake. Moral questions are primarily about approvals and disapprovals.
In doing so, we have a theory that makes sense of the way moral terms are actually used.
We still need to answer questions about what reasons for action exist. I would further argue that desires are the only reasons for action that exist, and that "approval" and "disapproval" themselves can be reduced to statements about desires and aversions.
Ultimately, it will turn out to be the case that morality is about promoting those desires (approvals) and aversions (disapprovals) that tend to fulfill other desires. But this is not a part of the meaning. The meaning only concerns reasons for action that exist, and leaves open the possibility of reasons for action other than desires.