adv.at (the) worst; if the worst comes to the worst
If we don't catch the bus, at the worst we'll just have to walk back.
No big deal. Let's go get more dough.
Don't be afraid, I will help you with your homework.
adj.serious; alarming; (used in the negative) terrible
It's nothing serious, just a scratch.
It's not so remarkable a success.
I just fell and it was no big deal.