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.

---

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

---

Etymology

Origin of invisible ink

First recorded in 1675–85

Example Sentences

Then the justices pitch a fit when the courts below don’t understand how to apply these orders written in invisible ink.

From Slate • Oct. 20, 2025

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

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

“But a close look at their skeletons and the similarities with pterosaurs became apparent, like invisible ink being held to the light.”

From New York Times • Oct. 5, 2022

As Washington shrewdly noted, the invisible ink would not only make “communications less exposed to detection” but also would “relieve the fears” of agents carrying the innocent-looking messages.

From "George Washington, Spymaster" by Thomas B. Allen