köken: From Middle High German īseren, īserīn, from Old High German īsarnīn, from Proto-Germanic *īsarnīnaz. Equivalent to Eiser (“iron”), older variant of Eisen + -en. Now reanalysable as Eisen (“iron”) + -ern, but historically eisern is itself one of the words that contributed to the development of this extended suffix -ern (see there).
aile: Eiserne Krone, eiserner Bestand, Eiserner Vorhang, eiserner Wille, Eisernes Kreuz, zum eisernen Bestand gehören
köken: From Old East Slavic твьрдъ (tvĭrdŭ), from Proto-Slavic *tvьrdъ, from Proto-Balto-Slavic *twírˀtas, from Proto-Indo-European *twerH-. Doublet of кварц (kvarc).
köken: From Proto-Indo-Aryan *dr̥ẓḍʰás, from Proto-Indo-Iranian *dʰr̥ždʰás, from Proto-Indo-European *dʰr̥ǵʰ-tó-s (“strong, firm, hard”), from *dʰerǵʰ- (“to be firm, strong, tough, hard”). Cognate with Old Church Slavonic дръжати (drŭžati, “to hold”), Lithuanian dir̃žti (“to harden, become tough”), Avestan 𐬛𐬀𐬭𐬆𐬰𐬀𐬌𐬌𐬈𐬌𐬙𐬌 (dar^əzaiieⁱti, “to attach”), English dry. The Sanskrit root is दृह् (dṛh) or दृंह्…