telltale

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. One who informs on another; a talebearer.
2. n. Something that indicates or reveals information; a sign.
3. n. Any of various devices that indicate or register information, especially:
4. n. A time clock.
5. n. Nautical One of the brightly colored lengths of yarn or ribbon attached to the shrouds, stays, or sails of a sailboat, serving to indicate wind direction relative to the boat's motion.
6. n. A row of strips hung above a railroad track to warn a passing train of low clearance ahead.
7. n. Sports A resonant metal strip, 24 or 30 inches (61 or 76 centimeters) high, across the bottom of the front wall of a racquets or squash court above which the ball must be hit.

Century Dictionary and Cyclopedia

1. n. One who officiously or heedlessly communicates information concerning the private affairs of others; one who tells that which is supposed to be secret or private; a blabber; an informer; a tale-bearer.
2. n. An indication or an indicator; that which serves to convey information.
3. n. A name given to a variety of instruments or devices, usually automatic, used for counting, indicating, registering, or otherwise giving desired information. Specifically— In organ-building, a piece of bone, metal, or wood, moving in a slot, which is so connected with the bellows as to indicate to the blower or player by its position the state of the wind-supply.
4. n. In ornithology, a tattler; a bird of the genus Totanus in a broad sense: as, the greater and lesser telltale, Totanus melanoleucus and T. fiavipes. See tattler, and cut under yellowlegs.
5. Disposed to tell or reveal secrets, whether officiously or heedlessly; given to betraying the confidences or revealing the private affairs of others; blabbing: as, telltale people.
6. Showing, revealing, or denoting that which is not intended to be known, apparent, or proclaimed: as, telltale tears; telltale blushes.
7. That gives warning or intimation of something: as, a telltale pipe attached to a cistern or tank.

Wiktionary

1. n. One who divulges private information with intent to hurt others.
2. n. slang Tattletale; squealer.
3. n. Something that serves to reveal something else.
4. n. music A movable piece of ivory, lead, or other material, connected to the bellows of an organ, whose position indicates when the wind is exhausted.
5. n. nautical 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.
6. n. nautical A mechanical attachment to the steering wheel, which, in the absence of a tiller, shows the position of the helm.
7. n. nautical 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.
8. n. engineering 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.
9. n. A bird, the tattler.
10. adj. revealing something not intended to be known

GNU Webster's 1913

1. adj. Telling tales; babbling.
2. n. One who officiously communicates information of the private concerns of others; one who tells that which prudence should suppress.
3. n. (Mus.) A movable piece of ivory, lead, or other material, connected with the bellows of an organ, that gives notice, by its position, when the wind is exhausted.
4. n. A mechanical attachment to the steering wheel, which, in the absence of a tiller, shows the position of the helm.
5. n. 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.
6. n. (Mach.) A machine or contrivance for indicating or recording something, particularly for keeping a check upon employees, as factory hands, watchmen, drivers, check takers, and the like, by revealing to their employers what they have done or omitted.
7. n. (Zoöl.) The tattler. See Tattler.
8. n. A thing that serves to disclose something or give information; a hint or indication.
9. n. (Railroads) An arrangement consisting of long strips, as of rope, wire, or leather, hanging from a bar over railroad tracks, in such a position as to warn freight brakemen of their approach to a low overhead bridge.

WordNet 3.0

1. adj. disclosing unintentionally
2. n. someone who gossips indiscreetly