DC is more problematic to switch than AC and a switch or relay designed for
AC must be derated (often massively) to use with DC.

But what about the reverse?

I have an automotive type relay rated 40A at 14V.

That should handle 10A (actually less) at 120VAC okay, yes?

Consequence of either failure to open or failure to close is near zero
(maybe a little wasted electricity). But I don't want it burning up
either. I would think something with a 40A DC rating is, if anything,
overkill. But the voltage is higher. However, I cannot imagine that the
contacts are left close enough together that the 120V (170Vpp) is an issue
as they'd be more likely to draw out and sustain an arc when used on the DC
it was designed for. So I think I am good.