The word “word”, as usually used, is not a term which is defined to only apply to things which have definitions.

Generally one can describe how people use a word. (Though, see “semantic primes”; there has to be some cycles in what words are defined using what words.)

I think the quotations around “define” were intentional in the comment you replied to. I think their point wasn’t to say something like the “undefinability of truth” paradox (the whole “truth is in the metalanguage” thing), but to say that it seemed to them that you were kind of sneaking in assumptions as part of definitions, or something like that, idk.

Congrats. What did you achieve with your definition?