Of unknown origin. There are various theories about its source:
- Might be related to the French and English re-.
- Or an alternative form of Middle Dutch er- and oor-; see German er-.
- Or come from a native Germanic adverb still present in modern German, her-.
Not separable. When forming past participles, it obviates the need to prepend with the prefix ge-.
- Adverbial and separable verbal prefix that indicates a movement