immigrant, foreigner, alien, outsider

For my ngram viewer search I decided to see which words for immigrants was more popular within American English.

I was surprised to see that “alien” had always been the more popular term to use, though I have to see this chart with bias as knowing that “alien” doesn’t only mean someone from another country being undocumented in their current country, but that in doctor’s terms people can have alien objects in their body, something can be an alien topic or subject, and that in general it just means that something’s unknown.

Still, there is a steep incline of alien and foreigner being used over immigrant within the English language after about 1920.

Kind of confused as to how it can be a popular term in American English before the 1600s though.

Outsider also became a more popular term after the 1950s, and immigrant is the only of the four words I searched that declined in popularity.