verunreinigen

The core idea of this root was

sieving

And based on that, it took on a figurative sense of discriminating, distinguishing.

There aren’t many German offspring but English has quite a few of them.
The most important branch is the one around the Latin cernere which was about separating, sifting, distinguishing.
Here’s a little overview over words in that branch:

• discern (“separate”)
• concern (“mix together, gathering together”)
• secret, secretary (“separate away”)
• excrete (“separate out”)
• discreet (“separated off”)
• discriminate (“separate off”)

And there are other surprising members as well, like these (and more):

• critic, criterion (“passing judgements, discernments”)
• certain (“distinguished with certainty”)
• ascertain (“make certain”)
• crisis (Originally in Greek: “moment of selection/judgement”)