(not) for a moment; (not) in the slightest; (not) under any circumstances
Used with a negative predicate to strongly deny any possibility or degree. Emphasizes that something is absolutely not the case, even momentarily or to the smallest extent.
I have never doubted him for a moment.
I can't even imagine such a thing in the slightest.
at any rate; at the very least; putting everything else aside
Used to set a minimum standard or to emphasize that even the most basic condition applies. Often implies that if nothing else, at least this much is true or should be done.
At the very least, once you've made a promise, you should keep it.
If you're a teacher at all, you can't say such a thing.