telltale

Etymology

From tell + tale.

noun

1. One who divulges private information with intent to hurt others.
   There were some ill-natured people —tell-tales—it seemed, in Tamai; and hence there was a deal of mystery about getting up the dance. 1846, Herman Melville, Typee
   The Chinese girls who saw me yesterday are telltales. I'd better wait till dark. 2008, Fleur Yano, Collected Writings of Flora Belle Jan, page 112
   Try to teach your child that there's a time to intervene and a time to mind your own business. Nobody loves a telltale. 2011, Elizabeth Grahamslaw, A Parents' Guide To Primary School
2. An indicator, such as a warning light, that serves to warn of a hazard or problem.
   A railroad company, which has properly erected a “telltale,” or signal board, to give warning of the approach of a train to a bridge and which lights the place at night by an electric light, is not responsible for injury caused at night by the “telltale” to a brakeman who had been passing under it at regular intervals for five weeks, though when injured he was standing upon a new car higher than those before used, and though he ad received no warning from the company as to the danger of standing upon such a car while passing under the "telltale". 1893, “Case No. 2: Phillips vs. The Railroad Co.”, in The Counsellor: The New York Law School Law Journal, page 63
   A float telltale to be provided which shall connect with indicator on first floor by a small chain run through 1-2 inch pipe and over pulleys well guarded against the weather. 1901, National Fire Protection Association, Proceedings - Volume 5, page 127
   For example, when trailers containing new automobiles were first piggybacked two areas of potential damage became evident: (1) diesel locomotive exhaust left a film of oil on the new autos; and (2) auto windshields could be scarred or cracked by the metal-tipped "tell-tales" which warn men atop trains of oncoming bridges or tunnels. Accordingly, automobiles aboard piggyback flats are usually coupled into the train 15 or more cars behind the locomotive; and telltales have been raised. 1960 November, David Morgan, “"Piggyback"—U.S. success story”, in Trains Illustrated, page 684
   Except for informational readout displays, each discrete and distinct telltale shall be of the color shown in column 2 of Table 2. 1980, The Code of Federal Regulations of the United States of America, page 150
   In order to resolve the discrepancy and permit the use of telltales in informational readout displays, the agency proposed the following requirement: Telltales and gauges incorporated into informational readout displays ( a ) Shall have not less than two levels of light intensity, a higher one for day and a lower one for nighttime conditions. (b) In the case of telltales amd gauges not equipped with a variable light intensity control shall have a light intensity at the higher level […] 1994, United States. National Highway Traffic Safety Administration, Federal Motor Vehicle Safety Standards and Regulations, page 26
3. (figurative) Something that serves to reveal something else.
   The telltale was the lipstick on his shirt collar.
   It supplies many useful links and tell-tales. 1898, George Saintsbury, A Short History of English Literature
   In most cases the event is shielded by a large mass and only telltales arrive on earth. Such telltales include neutrinos, or even some form of radiation. 2000, Dany Page, Jorge G. Hirsch, From the Sun to the Great Attractor, page 49
   It can be claimed that VC-dimension is to PAC-learning what finite telltales are to Inductive inference. 2003, Eric Martin, Arun Sharma, Frank Stephan, “On Ordinal VC-Dimension and Some Notions of Complexity”, in Ricard Gavalda, Klaus P. Jantke, Eiji Takimoto, editors, Algorithmic Learning Theory, page 54
   Just as small pieces of rock produce telltale directional noon holes, so do large pieces of rock on snow produce telltales: but these telltales are of rather a different kind. 2013, Harold Gatty, Finding Your Way Without Map or Compass
4. (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. (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.
   The sailmakers mistake can be an excellent way to lose a race as the telltale signals were disturbed and confusing. 1997, Patrick M. Royce, Royce's Sailing Illustrated - Volume 2
   If you turn toward the wind, the sail becomes undertrimmed, and the inside, or windward, telltale starts to rise and flutter as the flow is disturbed. 2011, J. J. Isler, Peter Isler, Sailing For Dummies, page 245
   The telltale shows if wind is flowing across the sail on every point of sail except a run. 2014, John Rousmaniere, The Annapolis Book of Seamanship, page 76
6. (nautical) A mechanical attachment to the steering wheel, which, in the absence of a tiller, shows the position of the helm.
7. (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. (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. A bird, the tattler.
10. A story or fable that has a moral or message.
    "Metamorphoses . . ." is the title of a book of telltales (or serialised fables) written by Lucius Apulei¡us, a neo-platonist priest in the second century A.D. 2012, Anna-Teresa Tymieniecka, The Origins of Life, page 130
    This telltale is not like the story that you put in the hands of your children, or those narrated by mothers in their children's bedrooms in Western Europe before sleep. This is a telltale that is not welcome but is forbidden to be distributed. 2018, Dawood Kaloti, The Telltale Leaflet: From Palestine to Stockholm

adj

1. Revealing something, especially something not intended to be known.
   His eye was blinking, a telltale signal that he was lying.
   He blushed when he approached, a telltale sign that he was happy to see him.