The union of two vowel sounds pronounced in one syllable, as in out, oil.

【语音】双母音(如out之ou、oil之oi)。

Two characters used to represent a single sound, as in hear, both.

【语音】二字母仅发一音者(如 speak 之 ea、both 之 th)。

Popularly, a ligature of two vowels, as in oesthetic.

【语音】(两母音相连之)结合字；母音连字(如 oesthetic 之 oe)。