Added 10 October 2026 nightmarious /ˌnaɪtˈmɛəɹi.əs/ adjective adjective ! Definition from Wiktionary (CC BY-SA). Pronunciation from Wiktionary, via Kaikki.org. More about nightmarious at Wordnik → Where our words come from → Having the qualities of a nightmare. Origin From nightmare + -ious. From Wiktionary, via Kaikki.org (CC BY-SA) Related Words: nightmarishnightmarelikenightmarymonsterfulhorrorousphantasmaldreamsomeaffreuxhorridsomesurrealscaresomehauntsome Back to today's word