Oennereeske are dwarves in Germanic mythology.
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In Friesland the Dwarfs are named Oennereeske in some of the islands Oennerbänske, and in Holstein Unnerorske.
The same stories are told of them as of the Dwarfs and Fairies elsewhere. They take away, and keep for long periods, girls with whom they have fallen in love; they steal children and leave changelings in their stead, the remedy against which is to lay a bible under the child’s pillow; they lend and borrow pots, plates, and such like, sometimes lending money with or even without interest; they aid to build houses and churches; help the peasant when his cart has stuck in the mire, and will bring him water and pancakes to refresh him when at work in the fields.
Source
THE FAIRY MYTHOLOGY BY THOMAS KEIGHTLEY (1850)