Niger UK /ˈnaɪ.d͡ʒə(ɹ)/US /ˈnaɪ.d͡ʒɚ/ noun3 •A country in West Africa, situated to the north of Nigeria. Official name: Republic of the Niger. •A major river in West Africa that flows into the Gulf of Guinea in Nigeria.From here we can see the River Niger in the distance running across town, a long gleaming diamond in the horizon. — 2023 •A state of Nigeria in the North Central geopolitical zone. Capital and largest city: Minna.