Fly-by-night

Origin of: Fly-by-night

Fly-by-night

Originally, from the late 18th century, this expression was an insulting term applied to women, implying that they were witches who flew by night on broomsticks. However, the meaning as we know it today of dubious or untrustworthy ethics dates from the early 19th century with the allusion to people who literally take off during the night to avoid paying rent, debts etc.