Two vowels that produce one sound. As in “aisle”. The “ai” is two letters but one sound. cf. improper diphthong (BBG 3.5).
Greek:
In Greek, the diphthongs are αι ει οι υι αυ ου ευ ηυ.
| αι as in aisle | αἴρω |
| ει as in eight | εἰ |
| οι as in oil | οἰκία |
| αυ as in sauerkraut | αὐτός |
| ου as in soup | οὐδέ |
| υι as in suite | υἱός |
| ευ, ηυ as in feud | εὐθύς or ηὔξανεν. |
| source | |
Hebrew:
See here.
