invisible ink

American  

[in-viz-uh-buhl ingk] / ɪnˈvɪz ə bəl ˈɪŋk /

noun

1. a fluid for producing writing that is invisible until brought out by heat, chemicals, etc.

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invisible ink British  

noun

1. a liquid used for writing that does not become visible until it has been treated with chemicals, heat, ultraviolet light, etc

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Etymology

Origin of invisible ink

First recorded in 1675–85

Example Sentences

In another, attributed to Aeneas the Tactician, a message hides dots of invisible ink over certain letters, which spell out the true message.

From Scientific American • Jun. 15, 2023

They may take part in a group experiment with invisible ink, where each of them can reveal a message that the ink hides by solving puzzles.

From New York Times • Apr. 27, 2023

Whether she's aware of the passages written in invisible ink in the margins and paragraph breaks is not for me to know or decode for my entertainment.

From Salon • Feb. 26, 2023

The search also yielded an invisible ink kit, documents with coded language and maps showing military bases, Myers said.

From Seattle Times • Jul. 28, 2022

“With invisible ink he could have just written the code on the front,” Reynie said.

From "The Mysterious Benedict Society" by Trenton Lee Stewart