病原: cause or source of a disease, pathogenesis, etiology

原発: Short for 原子力発電所. nuclear power plant / 原発: Short for 原子力発電. nuclear power generation / 原発: (medicine) primary (e.g. primary tumor)

原書: original document, original work / 原初: source, first, original / 厳暑: extreme heat

期限: deadline / 機嫌: mood, how one is feeling / 起源: origin / 紀元: era; AD

源流: source of something, especially a river

源三郎: a male given name

元一: a male given name

原水: / 減水: reduction in water level / 減衰: attenuation / 元帥: fleet marshall, fleet admiral

地雷原: minefield

幻影: an illusion, a vision; the image of something, such as in a memory or imagination; (medicine) a phantom, a phantasm: a perception of something that is not there