Adding a vowel (a, e, i, o, u, or y) to a word root to create a combining form allows two or more word roots to be joined to form a compound word. It also allows a word root to be joined with a suffix...

Adding a vowel (a, e, i, o, u, or y) to a word root to create a combining form allows two or more word roots to be joined to form a compound word. It also allows a word root to be joined with a suffix (ending of a word) to form a word. In addition, the vowel assists by making the term easier to pronounce. “O” is the most commonly used combining vowel.