The primary modern meaning is 'sheet metal' (metal rolled or hammered into thin sheets). The 'dagger' or 'sword' sense is archaic and refers to a blade made from such metal, now mostly encountered in historical contexts.
They cut sheet metal at the factory.
Ancient documents describe a dagger made of sheet metal.
Standard kanji spelling for sheet metal and the dagger/sword sense.
Abbreviated kanji spelling; less common but still used.
延べ (のべ, 'stretching, flattening') + 金 (かね/がね, 'metal'). Originally referred to metal that has been hammered or rolled into a thin sheet, and by extension a blade made from such metal.