Meaning

• One who divulges private information with intent to hurt others.

• Tattletale; squealer.

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

• Something that serves to reveal something else.

  "The telltale was the lipstick on his shirt collar."

• 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.

• 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.

Meaning

• Revealing something, especially something not intended to be known.

  "He blushed when he approached, a telltale sign that he was happy to see him."