Since around the turn of the 20th century, people are using
opposite less and
contrast more.
When I use the terms in my linguistic work, I use
contrast for when more than two things are being contrasted, and
opposite when there are just two. I doubt this change in general English has anything to do with English speakers becoming less binary, though. The rise of
contrast seems to be due to the rise of the phrase
in contrast to. (I won't share all the ngrams, but
you can look it up.)
But what is the downtrend for
opposite about? I tried looking at collocates in the
Corpus of Historical American English, and there are lots of different collocates if one compares the mid-19th and late-20th centuries. No clear explainers like a set phrase that's taken off. In the earlier data, there are more that have to do with politics, though: the
opposite parties, opposite doctrine,
opposite principles. Of course, in the 19th century, Americans fought a war against each other, so they really were opposed. The trends in the graph above, though, are not from American only. Maybe
opposite is going down in part due to the rise of
in contrast to. It's a possibly softer way to talk about opposed things.
Two other hypotheses that didn't pan out: the demise of
opposite does not correlate with a similar increase in
across from (that is, its prepositional use doesn't seem to have changed much), and there's barely any shift in the numbers for
antonym (it's just a line along the bottom of the chart).
