The belief that an airtight definition is required in order for a concept to be meaningful is just philosophically confused. That isn't how concepts work. Conceptual boundaries are always fuzzy, with confusing edge cases and ambiguities, and that's ok.

I'd challenge people who think definitions are necessary to grapple with coming up with a definition of a chair, in the form of a list of necessary and sufficient conditions. Make sure you don't exclude anything commonly thought of as a chair, or include anything not commonly thought of as a chair. For an extra challenge, come up with a definition most people would agree on. This endeavour will be a struggle.

And yet we manage to discuss chairs without difficulty. We have a generally understood concept of what we mean by a chair, with central examples like dining chairs or lounge chairs commonly held to be chairs. In the case of ambiguities of communication, we can clarify on a case by case basis ("Did you want me to take the ottomans to the other room too?")