accidental gap
Definition - (Aka hole in the pattern)

A word or other form that does not exist in a language but which should exist given the grammatical rules of the language.

For example, a common way of forming an English noun is by adding the suffix -al to a verb (e.g. dismissdismissal). There is an English verb describe, but there is no English noun describal, though theoretically such a word should exist. This absence, thus, is an accidental gap.

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