Nightmare/ˈnaɪtmer/ Definition 1 of 4Pro Tip 1/3Emotional Impact Nightmares can evoke strong emotions that may linger after waking up. I woke up shaking from a nightmare. Pro Tip 2/3Recurrent Themes Some nightmares are repeated with similar themes or scenarios. She keeps having nightmares about falling. Pro Tip 3/3Metaphoric Use 'Nightmare' can describe real situations that feel as bad as scary dreams. This traffic jam is a nightmare!