So the form as a whole was no longer seen as a plural, an instance of morphological leveling.
For example, if "geese" (the plural) became the word for "goose" (the singular) in a future version of English, a word geeses might become the licit plural form.
The ancient plural of child was "cildra/cildru", to which an -en suffix was later added when the -ra and -ru became unused.
Breeches is an example involving an old plural that did not use a suffix.
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