That is not true. More than a few laws have been created, enforced and had judgements executed on them that were vague as fuck. Part of a judge's job is interpreting the law. Defining your terms adds clarity, but that is not a requirement. And were it a requirement, then you just move the goal post to defining your definition.

You can add the definition:

Referring to yourself by the terms "lawyer" or "attorney" qualify as representing yourself as one who practices or may practice law.

Well what do you mean by "referring"? In writing? Verbally? In specific contexts? While soliciting business? Do you have to specifically say "I am a lawyer" or does implying you are one counts?

What do you mean by "yourself"? Your qualifications? Your clothing/appearance? Your mindset? Your future goals? Your idealized self?

You get the point. If you had to list every single way that a law could be broken, and define every single term within it (and within that, and within that, and within that, ad nauseum), then absolutley no law would be enforceable. Some amount 9f colloquial understanding of terms is required, as is intent.

That's why people argue about the actual meaning of the 2nd Amendment, for example. They argue about the framers' intent, context, verbiage, historical precedent, practicality, etc. and lawyers and judges OFTEN come up with conflicting interpretation. That doesn't mean that the law gets thrown out. It means that judicial interpretation, precedent, practicality, and stare decisis (i.e. deference to the decisions of a higher court) all have a part to play in law.