tail [OE] The base of the Old English word tail meant ‘hair’ or ‘hairy tail’ as on a horse, and was then extended to general use. The opposite side of a coin to heads has been tails since the 1680s or thereabouts—it is so called because it is the ‘reverse’ or ‘rear’ of the main or front side. A dog’s tail is a good indicator of its mood, and this has given us various expressions. Someone who appears ashamed or dejected has been described since the Middle Ages as having their tail between their legs. When the usual roles are reversed, the tail is wagging the dog [M20th]. As a verb [E16th] the original sense was ‘fasten to the back of something’, with the meaning ‘follow closely’ developing from this in the US at the beginning of the 20th century.