Laudator Temporis Acti

Homer, Iliad 13.39-41 (tr. Richmond Lattimore):

Τρῶες δὲ φλογὶ ἶσοι ἀολλέες ἠὲ θυέλλῃ
Ἕκτορι Πριαμίδῃ ἄμοτον μεμαῶτες ἕποντο
ἄβρομοι αὐΐαχοι...

At first I thought ἄβρομοι αὐΐαχοι might be a pair of asyndetic, privative adjectives, especially as there is a genuine example of that construction just a few lines earlier (at 13.37, ἀρρήκτους ἀλύτους), but further investigation convinced me I was wrong.

Lines 13.39-41 in Richmond Lattimore's translation:

But the Trojans, gathered into a pack, like flame, like a stormcloud,
came on after Hektor the son of Priam, raging relentless,
roaring and crying as one...

Walter Leaf ad loc.:

ἄβρομοι αὐίαχοι would at first sight appear to mean without noise or shouting (αὐιαχ- = ἀν-ϝιϝαχ-, ἀϝϝιϝαχ-? See Schulze Q.E. p. 65). But in Homer the noise of the Trojans is always contrasted with the silence of the Greeks; and if on entering into battle (Β 810, Γ 2, Δ 433-8) the Trojans were so clamorous, it is impossible to suppose that they became quiet when they were forcing the wall in their career of victory. Human nature too, to say nothing of the comparison of the storms, seems to insist that the words here must mean noisy. And so Ar. took them, ἀντὶ τοῦ ἄγαν βρομοῦντες καὶ ἄγαν ἰαχοῦντες. The ἀ- should rather be copulative, joining in noise and shout, as the existence of an 'ἀ- intensivum' is very doubtful. Etymologically this explanation (from sem-, sm-）seems unassailable; for similar cases see Schulze Q.E. p. 495 ff., and note on ἄξυλος, Λ 155. But it is hard to believe that such words were not ambiguous to the Greeks themselves when the negative ἀ- had driven competitors out of the field. We can only suppose that ἄβρομος and αὐίαχος were in common enough use to overcome the feeling that they were negative compounds.—It will be noticed that the variant ἀνίαχοι has good support; it is used also by Quintus (xiii.70) but it is impossible to say whether he took it to mean silent or noisy (of sheep following their shepherd from the pasture).

M.M. Willcock ad loc.:

ἄβρομοι αὐίαχοι: It is obvious that these adjectives are formed from βρέμω and ἰάχω, with a prefix ἀ-. What has divided scholars is whether the meaning is 'noisy' or 'silent'. ἀ- is most commonly a negative prefix (cf. note on Ἀβίων 6), but can confusingly also be positive or cumulative, e.g. ἄλοχος 'wife'. There is a similar uncertainty about the word ἀξύλῳ in XI 155.) Factors which have led scholars to prefer the explanation involving the less common prefix ('very noisy', 'loud shouting') are (a) that the poet made an explicit distinction at the beginning of Book III between the Greeks advancing silently into battle and the Trojans coming on with loud and barbarous cries, and (b) that the comparison with fire and storm in 39 suits noise rather than silence.

Richard Janko ad loc.:

ἄβρομοι αὐΐαχοι is a unique but old alliterative phrase (cf. 37). Aristarchus rightly took ἄβρομος as 'shouting together', with ἀ-intensive < *sṃ-, 'one' (cf. ἀολλέες) and psilosis. αὐΐαχος has the Lesbian doubling of intervocalic -ϝ- to replace metrical lengthening in a word originally shaped ˘˘˘¯, for *ἀϝίϝαχος; cf. ἔχευε < *ἔχε(ϝ)ϝε and ἀυάτα (ἀϝάτᾱ) for ἄτη, scanned ˘˘¯, in Alcaeus (Chantraine, GH1 159). Less probably, it is from *ἀν(α)-ϝίϝαχος, cf. Aeolic αὐέρυον < *αν(α)ϝέρυον (12.261, a similar verse): ἀνιάχω (Ap. Rhod.) is based on the old variant ἀνίαχοι here. Apion (frag. 5 Neitzel) thought the epithets mean 'silent' with ἀ-privative (cf. Ap. Rhod. 4.153). The Trojans charge noisily elsewhere (3.2, 4.433-8), unlike the more disciplined and unilingual Greeks (3.8). Their imminent victory would hardly make them silent now (so bT); they were just likened to fire and wind, which are loud.

At Apollonius of Rhodes, Argonautica 4.153, ἄβρομον clearly does mean silent: κῦμα μέλαν κωφόν τε καὶ ἄβρομον (a black wave, noiseless and silent).