Post History

This is not a proper answer as I cannot verify this etymology beyond Old Swedish "ohýris" meaning something like "immense".  I'm rather inclined to think that the word could be related to even older Old Norse "úhýrr" meaning "unfriendly looking"; you can readily see its reflections (in both meanings mentioned) in Danish and Norse.  But that's just a layman's guess which weighs less than the dictionary you are quoting.

However, the referenced dictionary entry does NOT indicate that the word originates from modern German and this should be cleared up.

On the very beginning of the entry, "1500-talet" suggests that the word existed in this form already in the 16th and 17th century, used about pests such as rats.  (To be applied to insects only later.) This kind of answers the question about age in itself: it is an old word in Swedish (per this dictionary).

The dictionary does suggest that the word was borrowed into Old Swedish from "German" but that must be referring to medieval precursors of German.

To decode the rest of the entry reliably, you'll probably need to go to approximately page 1280 (of the original numbering) and get familiar with all the language abbreviations.  That will show where a related word is suggested as the origin and where just as a sibling or a distant cousin.  The (modern) German word is ultimately given just as a distant cousin that many 1922 readers are likely to be fluent in, and thus quickly appreciate the semantic connection.  However, it's supposed to be a pretty distant connection, while a common ancestor is likely to be semantically mid-way.

For example, "fhty." stands for Old High German and "fsax." for Old Low German; we are talking about a 11th or 12th century (potentially) common ancestor of the modern Swedish and modern German word.  That's long ago, enough for long sequences of semantic shifts.  Even if you disbelieve the ancient borrowing, you should be prepared to see a whole string of semantic shifts over a millenium.  That's in itself quite normal.