ironside \ˈ ̷ ̷( ̷ ̷)ˌ ̷ ̷\noun 1.: a man of great strength or bravery 2. a.ironsidesplural, usually capitalized: any of various bodies of hardy veteran troops b.: a member of Cromwell's Ironsides cavalry during the English Civil War or of a similar force; broadly: a hardy veteran puritan soldier 3.ironsidesplural but singular or plural in construction: an ironclad ship