An extremely long time.
A mythical time in the infinite future that will never come.
Permanent, lasting; constant, perpetual.
We had to wait forever to get inside.
For all time, for all eternity; for a lifetime; for an infinite amount of time.
For a very long time, a seeming eternity.
Constantly or frequently.
Don't let it bother you; put it out of your mind.
I don't want to continue with this conversation (usually used in frustration or anger).
It doesn't matter.
A conventional reply to an expression of gratitude.
Absolutely not; I forbid it or it is impossible.