What is the term for the word formation process that results from blending parts of two or more existing words?

The term that describes the word formation process involving the combination of parts from two or more existing words is indeed blending. This process typically involves taking the beginning sounds or syllables of one word and combining them with the ending sounds of another, creating a new word that retains elements of each original term. For example, "brunch" is a blend of "breakfast" and "lunch."

Blending is distinct from affixation, which refers to the addition of prefixes or suffixes to the base form of a word to create new meanings. Diminution generally refers to creating a smaller or lesser form of a word, often for the purpose of expressing affection or familiarity, while compounding involves joining whole words rather than parts, such as "toothbrush" from "tooth" and "brush." Understanding these differences helps clarify why blending is the appropriate term for this specific word formation process.