Electromagnetism is one of how many interactions in nature ?
The word " electromagnetism " is a compound form of two Greek terms , ἢλεκτρον , " ēlektron " , " amber " , and μαγνήτης , " magnetic " , from " magnítis líthos " ( μαγνήτης λίθος ) , which means " magnesian stone " , a type of iron ore .