fly [OE] In Old English a fly, something that flies, was any winged insect. In the 17th century the clergyman Edward Topsell wrote of ‘the black flies called beetles’. A fly in the ointment is a minor irritation that spoils the success or enjoyment of something. The phrase goes back to a verse in the biblical book of Ecclesiastes, ‘Dead flies cause the ointment of the apothecary to send forth a stinking savour.’ To fly a kite [M18th] has had various incarnations in slang. It now means ‘to try something out to test public opinion’, but in the 19th century it was to raise money on credit. In the USA telling someone to go fly a kite is to tell them to go away. The flies on trousers or in a theatre come from the idea that they are only partly attached to their base, as if they could fly off.