In secret, in concealment, as in This agreement was concluded in the dark. [Early 1600s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
How to use in the dark in a sentence
Not even the most fertile imagination could have conjured a better monster-in-the-dark than IS.
They brand your right hand with a glow-in-the-dark stamp, and in you go.Partying With the Golden Globes Stars: Taylor Swift Cuts a Rug, Ben Affleck Holds Court, and More | Marlow Stern | January 13, 2014 | THE DAILY BEAST
Despite the eyes-in-the-dark logo and dramatic name, Jackson said they intended the site to teach rather than threaten.
Others call it the fisher, although it never fishes, while to the Indians it is the pekan—the killer-in-the-dark.Wild Folk | Samuel Scoville
Then into the next burrow and the next this Death-in-the-dark hastened.Wild Folk | Samuel Scoville