D defs.my
Entry 1 sense Webster, 1913

invisible ink

· in·vis·i·ble ink · IPA
01 n. A fluid that has no color in the visible spectrum, but may be detected under certain conditions, as under ultraviolet light. It may be use…
  1. 1.
    A fluid that has no color in the visible spectrum, but may be detected under certain conditions, as under ultraviolet light. It may be used to write notes not readable under normal light.