invisible

a. [ F. invisible, L. invisibilis. See In- not, and Visible. ] 1. Incapable of being seen; not perceptible by vision; not visible. Specifically: (a) Not visible due to an inherent property, such as lack of color; as, the invisible air; invisible ink; (b) hidden from view; out of sight; (c) Not perceptible due to lack of light; (d) Too small or too distant to be perceived; as, people on the ground invisible at cruising altitude. [ 1913 Webster +PJC ]

To us invisible, or dimly seen
In these thy lowest works. Milton. [ 1913 Webster ]

2. Hidden from the public; as, invisible transactions. [ PJC ]

3. imperceptible to the mind; as, differences invisible to most observers. [ PJC ]

Invisible bird (Zool.), a small, shy singing bird (Myadestes sibilons), of St. Vincent Islands. --
Invisible green, a very dark shade of green, approaching to black, and liable to be mistaken for it. [ 1913 Webster ]

n. 1. An invisible person or thing; specifically, God, the Supreme Being. [ 1913 Webster ]

2. A Rosicrucian; -- so called because avoiding declaration of his craft. [ Obs. ] [ 1913 Webster ]

3. (Eccl. Hist.) One of those (as in the 16th century) who denied the visibility of the church. Shipley. [ 1913 Webster ]

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 used to write notes not readable under normal light. [ PJC ]