*gheis-

The core idea of this root was:

excited, nervous, anxious

It’s the origin of the English words ghost and ghastly. The idea of ghost started from a sense of scary, but slowly took on the notion of disappearing.

German and English both used ghost/Geist as translation for spirit in the context of the bible.
In German, this became mainstream, so a Geist can be a scary ghost, but it’s also the word for the “mind” of a person.