A comment in another thread reminded me of another word that I don't really understand. When did the two words describing the automobile seat behind the driver become a single word: "backseat"? Pretty much all my life it has been "back seat," and then within the past year or two all I seem to see in print is "backseat."
Could a google Ngram do this? I'm none too sure of the search parameters though https://books.google.com/ngrams/graph?content=backseat,back+seat&year_start=1800&year_end=2019&corpus=26&smoothing=3&direct_url=t1;,backseat;,c0;.t1;,back seat;,c0
