What is the origin of 'sleep tight'?
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Definition of blue fire in US English:
blue fire
noun
Theatrehistorical
A blue light (typically produced by igniting a mixture containing sulphur) formerly used on the stage to create an unearthly or ghostly atmosphere, or to convey the effect of supernatural happenings; (hence attributive) sensational.
Origin
Early 19th century; earliest use found in London Literary Gazette.
