A dilithium hydoxyl is a chemical compound containing dilithium, oxygen, and hydrogen.
In 2152, a Retellian freighter expelled a cloud of dilithium hydroxyls and ionized pyrosulfates into the Enterprise's path, clogging the plasma vents and preventing the Enterprise from engaging its warp drive. (ENT: "Precious Cargo")
The Paulson Nebula is composed of 82% dilithium hydroxyls with magnesium and chromium. This allowed the USS Enterprise-D to use the nebular cloud to hide from the sensors of a Borg cube in 2366. (TNG: "The Best of Both Worlds")