cancrum

Etymology 2
From. The use of as a neuter nominative/accusative form may derive from a misunderstanding of the gender of the masculine accusative singular form. The term "cancrum oris" first appears in print in Observationes medicae de affectibus omissis (1649) by Arnoldus Boot as a translation of English "mouth canker" in a grammatical context that calls for an accusative singular, and so the form is ambiguous in this source as to the gender of the word. The hypothesis that the name cancrum oris originated in such a blunder is put forth by B. H. Coates (1826), who suggests the error first appeared in John Pearson's Principles of Surgery (1788, London, Chapter 13, Section 1 "Of the Canker of the Mouth", from page 262).

Noun

 * 1)  canker