1. revealing or indicating something that is meant to be hidden

1. a person who reports others’ wrongdoing or secrets
2. something that serves as an indicator or warning sign

Examples

• The muddy footprints were a telltale sign that someone had been in the garden.
• Her red eyes were telltale evidence that she had been crying.
• The teacher scolded the telltale for reporting his classmates.
• Nobody likes a telltale who constantly reports minor infractions.
• The smoke alarm serves as a telltale for potential fires.
• The dashboard warning light is a telltale that the engine needs attention.
• His nervous fidgeting was a telltale of his anxiety about the test.