alien
The term "alien" is often used in place of "extraterrestrial". In the sense that it derives from the Latin alienus (belonging to another person or place) this is appropriate. However, since "alien" can also mean repugnant or opposed to, it carries a negative connotation in contrast with the strictly neutral "extraterrestrial". It can also be argued that any kind of life or intelligence that is very different from the human variety is alien – whether it occurs on this planet or elsewhere.