An unreliable or irresponsible individual, particularly one not to be trusted in business dealings. Originating in the late eighteenth century to describe a person who evades creditors by sneaking away at night, this expression is now used both as a noun and as an adjective. However, according to Francis Grose’s Dictionary of the Vulgar Tongue (1796), the term was also once a derogatory name for an old woman accused of being a witch (flying at night). Much later it became British slang for a prostitute (who worked mostly at night), and by extension, a prostitute’s vagina.