Which process is defined as the creation of a word by removing an affix based on a mistaken relation to an existing word?

The process defined as the creation of a word by removing an affix based on a mistaken relation to an existing word is known as backformation. This linguistic phenomenon often occurs when speakers assume a word is derived from another word that is not its true source. A common example is the word "editor," from which the backformed verb "edit" was created. This happens when the original noun is perceived to be the result of the action that the removed affix represents.

In contrast, derivation involves creating a new word by adding affixes to a base word, which modifies its meaning or grammatical category but does not inherently involve a misunderstanding of the base's relationship. Inflection pertains to altering a word to express different grammatical categories such as tense, mood, aspect, or case, rather than creating new lexical items. Dissociation is not a widely recognized term in linguistic processes associated with word formation, which further clarifies backformation as the correct answer.