The headword adjective, in the accusative case, comes from Sophocles, Ajax 955; it appears in context at the end of the entry, where lines 955-6 are inaccurately quoted; and before that we have a slapdash version of a scholion thereto.
The phrase in Ajax here explained is: "the much enduring/daring man exposes on the surface his black-faced spirit" (web address 1). It is spoken by the Chorus in their protest against the cunning of Odysseus in winning the arms of Achilles, the decision that drove Ajax, who felt that he deserved them, to suicide. The scholion runs very clearly: "he exposes on the surface his black-faced spirit, as if it was already seen, not in the clear but in darkness, black and, as it were, hidden, treacherous and not straight-forward".
For similar uses of the adjective kelaino/s see kappa 1286, kappa 1285.
[1] The Homeric epithet for Odysseus is here used ironically. The use plays on the ambiguity of the verbs for enduring tla/w, tolma/w, which also mean 'I dare' (web addresses 2 and 3). We see a similar use of this ambiguity in the last surviving line of Sappho's famous fragment 31. At our first reading, we take her to mean by pa\n tolmato/n "all must be endured", i.e. she must go on suffering the sight of the beloved beside her husband. But of course, in writing the poem, with (at least in literary convention) the intention of sending it to the girl, she is simultaneously daring everything, "all must be dared".
[2] The verb in the passage is usually used in a very strong sense of insulting. This cannot be its meaning here, as recognized by LSJ (web address 4). Sophocles, in a passage of rhetorical figures, is using an etymological figure. Hybris is a recurrent theme in this play: see lines 153, 196, 304, 367, 560, 971, 1061, 1081, 1092, 1151, 1258. Just as hybris and the cognate verb u(bri/zw (together with its compound e)fubri/zw) come from u(pe/r, so the compound is here etymologically derived from e)fu/perqe 'on top, on the surface, (from) above' (web address 5). The two connotations, hybris and ‘insult’ (cf. Ajax 1385), remain strongly in the line. Odysseus has acted arrogantly and insultingly to a better man, and in doing so has show the black face of his hidden thymos or spirit. LSJ mistranslates the passage (web address 4).
[3] On h)/toi, used for emphasis rather than a disjunctive alternative, see J.D. Denniston, The Greek Particles, 553-54. The note refers to the play, not to the hero of the play.