[killerbat00]

The English usage is borrowed from French![0] However, it doesn't look like the original author was French[1]. I shouldn't be, but I am quite surprised to see that the apropos command as we know it is 43 years old!

[0] https://en.wiktionary.org/wiki/apropos [1] https://www.mankier.com/1/apropos.mandoc#History