Pluralising

Both of those are examples of the use of a possesive apostrophe though, you're not pluralising either. ❋ Cosmo7 (2009)

Although I do also tend to say "hippopotami": I hold that the pluralising rule -us - -i for words marked +classical is perfectly good English morphology, and I quite like the sound of other persons' teeth grinding. ❋ Unknown (2004)

The rector of Findon in 1276, Galfridus de Aspall, seems to have brought the art of pluralising to a finer point than most. ❋ E.V. Lucas (N/A)

Homer would find no difficulty in pluralising the mighty Hunter and the hare into huntsmen and hares when utilising a description originally referring to the constellation. ❋ Unknown (1862)

Monitor note: Other value/basic/essential ranges are available. letters passim): It was actually considered correct before the 1800s to use an apostrophe before the pluralising "s" if the word was of foreign origin. ❋ Unknown (2009)