The hunter poured the right amount of gunpowder from his powder-box to load his antique rifle.

powder 是名词，意思是"粉末"，这里特指"火药"。 box 是名词，意思是"盒子、容器"。 powder-box 是由 powder 和 box 组成的复合名词，指专门用来装火药的盒子，即"火药盒"。