This is from Cyr 7, 1, 7 I cannot understand in what meaning this participle is used: the translation renders it it as ‘advancing’, but no such meaning in dictionaries. The whole passage: ἡνίκα ἂν γένωνται τὰ κέρατα ἀναβαίνοντα κατ᾽ ἀντιπέρας τῶν πλαγίων τοῦ ἡμετέρου στρατεύματος, στραφέντες ὡς εἰς φάλαγγα ἅμα πάντοθεν ἡμῖν προσίασι μαχούμενοι.
Breitenbach, Xenophons Kyropädie für den Schulgebrauch Erklärt von Ludwig Breitenbach, 1875, Vol. 2. p. 86-87 explains it - paraphrased from me - as „after their wings march on in a long column toward the flanks of our army, they will front them“.
Looking at just that bit, I understand “κατ᾽ ἀντιπέρας τῶν πλαγίων τοῦ ἡμετέρου στρατεύματος” as the position that the enemy (them) is trying to get into.
The way I understand it (without context) is that the two wings of the “them” will be coming up on either side of the “us” forces as pincers. That’s when they’ll pull back from “us” into a dense mass, and engage as a body.
It seems pretty clear. But given that ol’ Ludwig apparently has a somewhat different understanding (maybe; I don’t really know what “front them” would mean), and has actually read the passage, probably I don’t get something.
the scene is: Kyros is speaking with Chrysantes, telling him : Do you see, the enemy marching on and their wings bending toward our troops (our flanks), taking position opposing our wings (= front our wings).
The situation is clear both from the Greek and from the Loeb translation adopted by Perseus.
Here’s the Greek: ἀλλὰ δῆλον, ἔφη ὁ Κῦρος, ὅτι ἡνίκα ἂν γένωνται τὰ κέρατα ἀναβαίνοντα κατ᾽ ἀντιπέρας τῶν πλαγίων τοῦ ἡμετέρου στρατεύματος, στραφέντες ὡς εἰς φάλαγγα ἅμα πάντοθεν ἡμῖν προσίασι μαχούμενοι.
And here’s the Loeb translation: “Well,” answered Cyrus, “it is obvious that just as soon as the wings now advancing in column get directly opposite the flanks of our army, they will face about so as to form front and then advance upon us from all three sides simultaneously; for it is their intention to close in on us on all sides at once.”
The Loeb translation, by Walter Miller (“ol’ Walt” as Joel might call him), is inevitably dated (1914) but to judge from a few samples is uniformly excellent. The concluding phrase here, however, seems gratuitously expanded, though of course Greek tends always to be more densely expressed than English.
There’s an interesting Wikipedia article on Miller (philologist).
further, in 7, 1, 23 the adv ἅνω is used in the sense of ‘further’ which is not registered in dictionaries.
Interesting question. At first it seemed really straightforward, probably because in English we’d happily say “come up” to mean “advance, go forward” (“this guy came up to me and said…”), but as you say, the dictionaries don’t support that meaning in Greek for either the verb or the adverb.
Maybe it’s because of the use of “horn” in both passages to describe what we’d call the wings or flanks… If animals attack with their horns they push them up, right? Not my field of expertise to be honest 
That’s why it’s conceived as a position that they’re getting into. IMO, anyway. Assuming that they aren’t on a hill.
it’s clear they are not on a hill.