You learn something every day, they say, especially if you visit this board.

I recall being taught that æ is a diphthong. From what I've read above and in several online dictionaries, I now gather that diphthong has the following meanings:

1. Two vowels in which there is a perceptible movement from one sound to another, e.g oi in noise. Sometimes called a "proper diphthong".

2. A vowel digraph in which there is only one sound, e.g. ai in rain. Sometimes called an "improper diphthong".

3. A ligature

Given its etymology ("two voices/sounds") I gather definition #1 is the original and most common.

Is that a fair summary?