...and you just can't get it. It's so annoying.

I'm looking for the word that says it is "up to" a person to do something. The word "incumbent" keeps popping into my head, but I know that's not it at all.

And when this happens, you can't look in a dictionary - where do you start looking?

This is so frustrating. Can somebody put me out of my misery and tell me what the word is?

you *can say: "It is incumbent upon so and so to do such and such."

Shucks, belM. You shouldn'ta said "incumbent." Now I can't think of anything else, either.

Voluntary?

bel, is this something behooving, or is it just de rigueur?

It's the duty of that person?

beholden?