iron-sided
/ˈʌɪənsʌɪdɪd/adjective
1Tough, hardy; unyielding, inflexible.
2Of a material object: having sides which are made of iron, or which are as strong as iron.
3Of a warship: having sides strengthened with plates of iron or steel; = ironclad. Compare Ironside. Now historical.
Origin
Mid 17th century; earliest use found in John Gauden (c1599–1662), bishop of Worcester. From iron + sided, after Ironside.