This could get head scratchy.
If "nothing has ever been defined." then the word "defined" hasn't been defined (along with "nothing", "has", "ever" and "been").
"Nothing has ever been defined." is right next to "This sentence is a lie." as far as useless sentences go.
Which is to say, they both illustrate a paradox that arises from a misunderstanding of how language works.
Obviously language works to some extent, even with protracted arguments of the precise meaning of a given word.
And since languages are composed of words - it must be the words that are doing all the work?
We can easily see why mathematicians and philosophers would have felt that if only we can nail down the meaning of a word, we could bypass all these pointless
internet forum arguments and really make some proper progress.
Fast forward a couple of millennia and no mechanism has yet been proposed that would allow anyone to unambiguously specify a single meaning for any word.