Noun
An ink, invisible on application or soon thereafter, that can later be rendered visible by some process, such as exposing it to heat.
Synonym: (dated) sympathetic ink
An ink used in pranks that is visible at first but soon disappears.
Source: en.wiktionary.orgPoetry is written with tears, fiction with blood, and history with invisible ink. Carlos Ruiz Zafón
The pages are still blank, but there is a miraculous feeling of the words being there, written in invisible ink and clamoring to become visible. Vladimir Nabokov
i sometimes felt as if these marks on my body were a kind of code, which blossomed, then faded, like invisible ink held to a candle. But if they were a code, who held the key to it? I was sand, I was snow-written on, rewritten, smoothed over. Margaret Atwood
When life gives you lemons you squeeze them, hard. Make invisible ink. Make an acid poison. Fling it in their eyes. Austin Grossman
A similar strategy is to issue prisoners with writing paper ruled with a water-soluble ink that runs in contact with water-based invisible ink. Source: Internet
It also includes an ultraviolet light and changeable invisible ink nib for viewing messages written in the ultraviolet ink. Source: Internet