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Caesar and a German Unicorn? | Beachcombing’s Bizarre History Blog
quidquid bene dictum est ab ullo, meum est
quidquid bene dictum est ab ullo, meum est
@Beachcombing’s Bizarre History Blog
rogueclassicism 
I’m pretty sure it’s used for both antlers, like the German singular terms “Gehörn”, “Geweih” and “Gestirn”. Same in Latin: we have e.g. “cornua” for both horns of the crescent moon, but also “cornu” for the crescent moon itself. According to the etymology “cornu” probably stems from an old dual form, like “genu” (“knee”, but also “pair of knees”). So I assume that the proper translation of “cornu” in this passage is “pair of horns”.
We could add one thing: We know that Caesar – i.e. most probably Caesar or one of his scribes, not a later interpolator – used the description of the elephant from the Greek Physiologus (ch. 43) for the deer, simply because he mistook ελεφας for ελαφος. (The same mistake was made by Pliny.) The descriptions are extremely similar; cf. e.g. Phys. gr. 43.16 sq. about the missing joints. But did Caesar also use the description of the unicorn from Phys. gr. 22? Probably not, because they are nothing alike; cf. 22.4 sq.: ἓν δὲ κέρας ἔχει, μέσον τῆς κεφαλῆς αὑτοῦ. Sure, there’s “one horn” and “in the middle of the head”, but that’s generic: there’s no “forehead”, no “between the ears”, no detailed description of the antlers. So I suspect that we can rule out the Physiologus as Caesar’s source here.