Anyway, it sounds Greek. Indeed, it comes from the Greek abussos (bottomless) as a- (without) + bussos (bottom). It seems that bussos perhaps is used with special reference to the bottom of the sea, which would make sense--in modern English the abyssal plain is the vast, flat bottom of the sea to which no light can penetrate. A simple, reasonable derivation.
Ethiopia used to be called Abyssinia--any relation to the above definition of abyss? No--it comes from Arabic, according to Wikipedia.
I didn't know that Abyssinia was Ethiopia; the only time I had seen it before was in Samuel Coleridge's memorable poem Kubla Khan, the end of which is reproduced below:
- It was a miracle of rare device,
A sunny pleasure-dome with caves of ice!
- A damsel with a dulcimer
In a vision once I saw:
It was an Abyssinian maid,
And on her dulcimer she played,
Singing of Mount Abora.
Could I revive within me
Her symphony and song,
To such a deep delight 'twould win me,
- That with music lound and long,
I would build that dome in air,
That sunny dome! those caves of ice!
And all who heard should see them there,
And all should cry, Beware! Beware!
His flashing eyes, his floating hair!
Weave a circle round him thrice,
And close your eyes with holy dread,
For he on honey-dew hath fed,
And drunk the milk of Paradise.