The definition is Warship, referring to an ironclad — a type of armoured warship. The wordplay is a charade: IRON means "press" (as in a clothes iron), and CLAD means "covered". Put them together and you get IRON-CLAD. The reviewer notes that strictly speaking, the noun "ironclad" (warship) is usually one word, while the hyphenated "iron-clad" is more of an adjective meaning certain or impregnable.