A thorough look at the German verb "lassen". We'll learn its core meanings, see what it has to do with passive voice and explore the various prefix versions.
The core idea of this root was:
letting go, slacken off, relenting
And we can still see this sense in the English offspring, like last, let, lenient, latter or late.
By the way, the words relax and and release, though they would fit in here, apparently come from a different root.