No, but meaning is always contingent. It really can be the case that something has meaning because or arising out of our agreements that supply that meaning. [It's too deep a rabbit hole to get into the contingent nature of meaning here.]So "meaningful" is just a statement that words have definitions.
It's not circular. An imagined DM who is hostile to 5e* could exercise themselves to say things that they've decided are meaningless. That is going to create forseeable dissonances for their players.Again, I note the irony that to preserve the construction of "meaningful" you're busily diluting the concept to one that is largely meaningless. A blue cloak is meaningful because blue means blue. And things matter because if they are said then they matter. How do we know they matter? They were said, so they must. Again, circles.
The social contract between players and DM under 5e* is that whatever DM narrates, players may respond to as if it mattered. My imagined hostile DM sets out to break that contract.
DM The whole room is suddenly engulfed in blazing fire.
P Gods, I need to get out! Help me someone.
DM Nah, the fire doesn't matter. It's just colour.