Something that's telltale accidentally relays important information. A wise parent can tell who ate the last of the birthday cake by the telltale chocolate smudges on the culprit's face.

The telltale dark circles under your teacher's eyes betray how little sleep he got last night, and a telltale bulge in a shopper's pocket is sometimes enough for a store owner to suspect she's a shoplifter. If it's telltale, its very presence reveals something. A famous occurrence of telltale, although it's spelled with a hyphen, is Edgar Allen Poe's story "The Tell-Tale Heart," about a murderer who imagines he's betrayed by the telltale beating of his victim's heart.

Definitions of telltale

adj disclosing unintentionally

“a telltale panel of lights”
“a telltale patch of oil on the water marked where the boat went down”
revealing, telling
informative, informatory
providing or conveying information

n someone who gossips indiscreetly

blabbermouth, talebearer, taleteller, tattler, tattletale
Type of:
gossip, gossiper, gossipmonger, newsmonger, rumormonger, rumourmonger
a person given to gossiping and divulging personal information about others

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