Back-formation

Back-formation is a type of word formation by analogy. Back-formation occurs when speakers of a language assign a regular derivational structure to a word, although a part of this structure, namely the base, did not previously exist. If this new base becomes a word of the language, it is called a back-formation.

Examples
Speakers of English have reinterpreted the root compound baby-sitter as being a synthetic compound, i.e. consisting of the base baby-sit and the suffix -er, and on the basis of this noun they have coined the verb to baby-sit. Another example is self-destruct from self-destruction.

Comment
In the literature, the existence of back-formation is taken as evidence for a word-based morphology.

Link
Utrecht Lexicon of Linguistics