An imaginary disease.
An imaginary disease that does not and will not ever exsist!
The opposite of imaginary could be real, actual, or existing.
An imaginary line around which an object rotates.
Cooties is an imaginary disease. Nobody really has cooties or can catch them.
contagion
An imaginary line in space could refer to an axis of rotation or an orbit path. For example, the Earth's axis is an imaginary line around which it rotates, while the orbit path of a planet around the Sun could be considered an imaginary line in space.
No. They are synonymous terms.
immunity
The imaginary line in a film preserves the audience's visual point of view. It is a director's axiom for camera placement, and not one dictated by the script. The overarching notion that contains the imaginary line is known as the '180 degree rule'.You can read more about it and other cinematic terms, below.
Relapse
No. A complex number consists of a real part and a imaginary part. If the real part equals zero, there is only the imaginary left and you could therefor argue that it is an imaginary number (or else it would still be a complex number -with a real part=0)