sklēros

BDAG sorts σκληρός by what it qualifies: things ("hard, rough", the ἄνεμοι σκληροί of Jas 3:4), persons ("harsh, stern", Mt 25:24), speech ("harsh, unpleasant", Jn 6:60 and the σκληρά of Jd 15), and the impersonal predicate σκληρόν σοι, "it is hard for you", at Ac 26:14. LSJ documents the full classical range from the physically hard, dry, and unyielding through the transferred senses harsh, stubborn, and unfeeling, together with the impersonal and adverbial constructions. TDNT and EDNT treat the adjective inside the σκληρ- group and observe that the theological weight of the family attaches chiefly to σκληρύνω, σκληροκαρδία, and σκληροτράχηλος under Septuagintal influence, where σκληρός itself renders קָשֶׁה and its kin for oppressive labor and stiff-necked people, while the adjective in the New Testament keeps its general secular range. On Jn 6:60 the main commentators (Barrett; Brown; Schnackenburg) take σκληρός as "offensive, unacceptable" rather than "unintelligible", since the complaint is followed by defection rather than by a request for clarification. On Ac 26:14 the clause πρὸς κέντρα λακτίζειν is a Greek proverb attested in Pindar, Aeschylus, and Euripides, and Barrett notes that its placement in the speech before Agrippa suits that retelling's Hellenistic address. The occurrence at Ac 9:5 is text-critically secondary: Metzger records that no early Greek witness carries the clause there and that it entered by assimilation to 26:14 through the Latin tradition, so critical editions print it only at 26:14. Jd 15 quotes 1 Enoch 1:9, where τὰ σκληρά are the insolent things the ungodly have spoken against God (Bauckham).