A dream arousing feelings of intense fear, horror, and distress.
An event or experience that is intensely distressing.
A demon or spirit once thought to plague sleeping people.
[Middle English, a female demon that afflicts sleeping people : night, night; see night + mare, goblin (from Old English; see mer- in Indo-European roots).] night'mar'ish adj., night'mar'ish·ly adv., night'mar'ish·ness n.