1.
not less than :
It'll cost at least 500 dollars.
She must be at least 40.
Cut the grass at least once a week in summer.
I've known her at least as long as you have.
2.
used to add a positive comment about a negative situation :
She may be slow but at least she's reliable.
3.
even if nothing else is true or you do nothing else :
You could at least listen to what he says.
Well, at least they weren't bored.
4.
used to limit or make what you have just said less definite
SYN anyway :
They seldom complained—officially at least.
It works, at least I think it does.