The quest for the biblical unicorn (Commentary on Job 39:9)

One of the curious features of the Greek version of the Old Testament is the appearance of the word μονόκερος, literally 'a one-horned [creature]', which the King James translators translated as 'unicorn,' a word that at least modern English speakers associate with a mythical and fanciful beast. This translation has mystified many. The eighth-century Armenian exegete Stepanos of Siunik, whose fragmentary commentary on the book of Job I have been translating here has this to say about the appearance of 'unicorn' in Job 39:9:

Symmachus translates it as ‘saw-horn’ (սղոցեղջիւր). There is a lake in the land of the Philistines from which every venomous beast and reptile of the fields drinks, and in which birds and quadrupeds cannot approach until the unicorn comes and heals the water with its horn. It drinks first. Anyone who wishes to hunt it must place in its path an adorned and perfumed virgin. It is in this way that they capture it.

Symmachus was a Jewish translator of the scriptures into Greek. I'm not sure which Greek word would correspond to 'saw-horn' here. It should be a calque on πρινόκερως, a word I've been unable to find in any extant Greek text. That word though is very close to ρινόκερως, 'rhinoceros,' literally, a nose-horn, so perhaps that is our biblical unicorn.