telltale

A movable piece of ivory, lead, or other material, connected to the bellows of an organ, whose position indicates when the wind is exhausted.

A length of yarn or ribbon attached to a sail or shroud etc to indicate the direction of the flow of the air relative to the boat.

One who divulges private information with intent to hurt others.

Something that serves to reveal something else.

An indicator, such as a warning light, that serves to warn of a hazard or problem.

A mechanical attachment to the steering wheel, which, in the absence of a tiller, shows the position of the helm.

A compass in the cabin of a vessel, usually placed where the captain can see it at all hours, and thus inform himself of the vessel's course.

A machine or contrivance for indicating or recording something, particularly for keeping a check upon employees (factory hands, watchmen, drivers, etc.) by revealing to their employers what they have done or omitted.

A bird, the tattler.

A story or fable that has a moral or message.

Revealing something, especially something not intended to be known.