Which pair of terms refers specifically to a sound produced when transitioning between two vowels?

The term that specifically refers to a sound produced when transitioning between two vowels is "diphthong." A diphthong is a complex vowel sound that begins with one vowel sound and glides into another within the same syllable. This combination creates a distinct sound that combines the qualities of both vowels, making it different from a single vowel sound.

For example, in the English word "coin," the vowel sound transitions from the 'o' sound to the 'i' sound, illustrating how diphthongs function in spoken language. Understanding diphthongs is important in phonetics and phonology, as they show how vowel sounds interact and change during pronunciation, impacting aspects such as accent and dialect.

In contrast, a diacritic refers to a symbol added to a letter that alters its pronunciation or distinguishes it from a similar letter; a monophthong is a single, pure vowel sound without any glide; and a phoneme is the smallest unit of sound in a language that can distinguish words. Each of these terms describes different aspects of sound and pronunciation, but only diphthong specifically denotes the blending of two vowel sounds.