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English definition of “nightmare”

nightmare

noun [C]    /ˈnɑɪtˌmeər/
a very upsetting or frightening dream , or an extremely unpleasant event or experience nightmarish    /ˈnɑɪtˌmer·ɪʃ, -ˌmær-/ adjective a nightmarish traffic jam
(Definition of nightmare noun from the Cambridge Academic Content Dictionary © Cambridge University Press)
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