a place name, such as that of Konan city in Shiga prefecture / Hunan province in China

Huainan

a southern sea / (specifically) South China Sea / Short for 南海道(なんかいどう) (nankaidō)

southern Fujian (a region of Fujian, China)

one's second son

(historical) Syonan, Singapore (an island and city-state in Southeast Asia), as part of the Empire of Japan

difficult problem

dense, abstract, abstruse, recondite

obscurity

Shōnan, a region along the coast of Sagami Bay