How do you spell Contagious

Available Definitions:
1)  a. - Communicable by contact, by a virus, or by a bodily exhalation; catching; as, a contagious disease.
2)  a. - Conveying or generating disease; pestilential; poisonous; as, contagious air.
3)  a. - Spreading or communicable from one to another; exciting similar emotions or conduct in others.