[seszett]

Chalant is the present participle of the (disused) verb "chaloir", which means "to matter to someone", "to be important (to someone)".

It's only used anymore in the words "nonchalant" (someone to which things don't matter much) and the expression "peu me chaut" (it matters little to me).

But although "nonchalant" has a clear meaning, the meaning of "chalant" wouldn't be as obvious, since while it's easy to not care about things generally, "generally caring about things" is just the normal state of a person. It's the same reason you don't often hear about a stoppable force or a wieldy tool.

[touisteur]

Bien achalandé ?

[seszett]

Chaland is something unrelated, it's a slow delivery barge from which derive two meanings, one for a shop being well-stocked (bien achalandé, because it's well served by the barge) and the other for visiting things at a leisurely pace (because the barge is slow and makes many stops).