What is the term for the mysterious unstressed vowel in the word "banana"?

The term for the mysterious unstressed vowel in the word "banana" is known as a schwa. The schwa is represented by the symbol /ə/ in phonetics and is characterized by its weak, neutral sound that occurs in unstressed syllables. In "banana," the first and third 'a' sounds are unstressed and pronounced as schwas, resulting in a softer and less distinct sound compared to the stressed syllable in the middle.

Understanding this concept is essential because it highlights the behavior of vowels in different syllabic roles. The schwa is the most commonly used vowel sound in English and appears in many words, often in unstressed positions, which contributes to the rhythm and melody of speech. Other terms like root vowel, affine, and diphthong have different meanings in phonetics and linguistics and do not accurately describe the sound present in unstressed syllables like those in "banana."