Sentence:  The corpus of related texts tells us that within rural society it was not improbable for your neighbour's envy of your fine cattle to take the form of a <WSD>"mara</WSD>". 
Meaning of the word marked with <WSD> tags:  A nightmare; a spectre or wraith-like creature in Germanic and particularly Scandinavian folklore; a female demon who torments people in sleep by crouching on their chests or stomachs, or by causing terrifying visions.