It’s because -us is the Latin second declension nominative singular, and its nominative plural is -i. People educated enough to know the -us/-i pattern (cactus/cacti, alumnus/alumni, stimulus/stimuli) but unaware that “octopus” is Greek and has an irregular stem are likely to misapply the Latin pattern.
It’s because -us is the Latin second declension nominative singular, and its nominative plural is -i. People educated enough to know the -us/-i pattern (cactus/cacti, alumnus/alumni, stimulus/stimuli) but unaware that “octopus” is Greek and has an irregular stem are likely to misapply the Latin pattern.
I thought as much, but was never sure. Could’ve developed more naturally, like from Romans in Britain, for all I knew.