In Nietzsche's Beyond Good and Evil, he has the following well-known line:
Wer mit Ungeheuern kämpft, mag zusehn, dass er nicht dabei zum Ungeheuer wird. Und wenn du lange in einen Abgrund blickst, blickt der Abgrund auch in dich hinein.
Whoever battles monsters should see to it that in the process he does not become a monster himself. And when you look long into the abyss, the abyss also looks into you.
Original text and translation from this post.
What would be the best word for abyss in this usage? My initial thoughts for words used in the classical period were barathrum, chasma, or profundum. I'm not opposed to later words like abyssus, but I prefer classical when possible. Does one of the former three best capture abyss in the way that Nietzsche meant?