Which part of a diphthong is referred to as the onglide?

In the context of phonetics, a diphthong is characterized by a smooth, gliding transition between two vowel sounds within the same syllable. The onglide refers specifically to the initial or starting component of the diphthong. In this situation, the first vowel sound is identified as the onglide because it serves as the primary vocalization that begins the transition to the second vowel sound. This structure is essential for understanding how diphthongs function in speech and helps in accurate pronunciation and phonetic transcription.

For example, in the diphthong /aɪ/ (as in "my"), the onglide is /a/, leading into the second vowel sound /ɪ/. Recognizing the role of the onglide aids in differentiating between various diphthongs and their phonetic characteristics, enhancing both auditory discrimination and speech production skills.