Why is the ninth month called September?
c.1300, fantum "illusion, unreality," from Old French fantosme (12c.), from Vulgar Latin *fantauma, from Latin phantasma "an apparition" (see phantasm). The ph- was restored in English late 16c. (see ph). Meaning "specter, spirit, ghost" is attested from late 14c.; that of "something having the form, but not the substance, of a real thing" is from 1707. As an adjective from early 15c.
phantom phan·tom or fan·tom (fān'təm)
Something apparently seen, heard, or sensed, but having no physical reality.
An image that appears only in the mind; an illusion.
A model, especially a transparent one, of the human body or of any of its parts.
Resembling, characteristic of, or being a phantom; illusive.