Extraterrestrials
If you mean illegal alien, it would be an undocumented worker(person).
An alien, immigrant, incomer, outsider, stranger, outlander
The opposite of native would be immigrant, alien, colonist, barbarian or invader.
A more polite alternative for "idiot" could be "fool" or "simpleton".
My school is nicer than other schools in the district. In fact, my school is the nicest in the whole country.
The root word for "inalienable" is "alien." "Inalienable" means unable to be taken away or transferred from its possessor, reflecting the sense of being foreign to or incompatible with something or someone else.
A nicer word for theft is embezzlement.
nicer
No nicer is wrong English, however you cannot add "-er" to the end of nice.
Nicer
improving
Subsequently, later, next...
nicer
Push or nudge.
nicer, nicest
Nicer euphimism for the "f" word.
SACKED
The noun "alien" is a singular, common, concrete noun, a word for a person. The word "alien" is also an adjective.