eukairos

Every standard lexicon derives εὔκαιρος from εὖ ("well") plus καιρός ("opportune time, season") and glosses it "well-timed, seasonable, suitable" (BDAG; LSJ; Louw-Nida place the family in the semantic domain of favorable time). Classical and Hellenistic usage runs wider than time alone, extending to strategically situated places (Polybius; 2 Maccabees 15:20). The adjective occurs twice in the New Testament. At Mark 6:21 the mainstream commentary tradition (Collins, Marcus, France, Cranfield, Hooker) reads "an opportune day" as the moment that finally enabled Herodias's plot, part of an ironic thread Mark runs through his cognate uses; an older rendering "festal day" (Pallis; the Moffatt and Goodspeed versions) is now generally rejected. At Hebrews 4:16 (εἰς εὔκαιρον βοήθειαν, "for well-timed help") Moffatt, Attridge, Ellingworth, Koester, and Cockerill stress the qualitative sense of help that arrives precisely when needed, with the Greek Old Testament of Psalm 104:27 (God gives creatures their food "in due season") as background. A once-influential claim, associated with Oscar Cullmann and Gerhard Delling, that the καιρός root carries a fixed qualitative theology of time distinct from χρόνος was decisively criticized by James Barr (Biblical Words for Time, 1962); current lexicography treats εὔκαιρος as ordinary Koine Greek whose theological weight, where present, comes from context rather than from the root.