TELLTALE

revealing, telling, telltale

(adjective) disclosing unintentionally something concealed; “a telling smile”; “a telltale panel of lights”; “a telltale patch of oil on the water marked where the boat went down”

tattletale, tattler, taleteller, talebearer, telltale, blabbermouth

(noun) someone who gossips indiscreetly

Source: WordNet® 3.1

Etymology

Noun

telltale (plural telltales)

One who divulges private information with intent to hurt others.

Synonyms: blabbermouth, gossip, rumormonger, talebearer, Thesaurus:gossiper

(chiefly, US, slang) Tattletale; squealer.

(figuratively) Something that serves to reveal something else.

(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.

(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.

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

(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.

(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.

A bird, the tattler.

Adjective

telltale (comparative more telltale, superlative most telltale)

Revealing something, especially something not intended to be known.

Source: Wiktionary

Tell"tale`, a.

Definition: Telling tales; babbling. "The telltale heart." Poe.

Tell"tale`, n.

1. One who officiously communicates information of the private concerns of others; one who tells that which prudence should suppress.

2. (Mus.)

Definition: 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.

3. (Naut.) (a) A mechanical attachment to the steering wheel, which, in the absence of a tiller, shows the position of the helm. (b) 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.

4. (Mach.)

Definition: 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.

5. (Zoöl.)

Definition: The tattler. See Tattler.

Source: Webster’s Unabridged Dictionary 1913 Edition