From the science I am in, computational cognitive neuroscience, and also structural formal linguistics, the definition of a "lie" is anything somebody calls a lie. Our job is not to define the undefinable but rather to understand how the internal brain/neural machinery can do such things as calling something a lie and finding agreement or disagreement (or even "'don't care' but 'I understand what you are saying'") with other people. Empirical science about actual behaviors but including, and not denying the existence of, verbal behavior. See de Saussure (late 1800s).

https://medium.com/liecatcher/100-billion-sources-of-hate-between-your-ears-d34baf503c98

That said, one of the most profoundly important empirical observations we can make about human natural language is precisely that we can easily write nearly universally accepted dictionary definitions of every word in use in any language. Explain that without a computation model! We see gravity when all you see is friction. It's a positive thing.

Lies are just another object worthy of scientific study, even like pond scum.

We are not accusing anybody of anything except they ignore the very medium for their messaging between their brains while they pretend to be understanding how their brains work. (They can show you the feather falling more slowly than the cannon ball and use that to say you know nothing of gravity). As we show, and you can experience with www.truthcourt.net if you sign up and actually serve as a juror, how you can dissect any truth or lie and understand its parts as massive assemblies of predications of fundamental predication (advanced perceptron) computation units. This is anything claimed to be a "truth" or anything claimed to be a "lie". You can also use a similar technique to dissect anything claimed to be a "dog." No difference in the empirical science.

Here is a bit of proof of that based on a study of the medium of natural language in brain to brain communication that can be observed likely any other object of scientific study:

https://medium.com/liecatcher/how-your-brain-computes-41ebe7428ff9