What does the French word dah mean?

There is no French word "dah". It's possible you're thinking of a word with a similar spelling or sound, like:

* "Da" - which is an informal way to say "yes" in French.

* "D'accord" - which means "agreed" or "okay".

* "D'ailleurs" - which means "besides" or "moreover".

* "Dès" - which means "from" or "as soon as".

Can you provide more context about where you encountered this word? This might help me understand what you're looking for.