difficult problem

dense, abstract, abstruse, recondite

obscurity

Benin (a country in West Africa)

Henan (a province of China; capital: Zhengzhou)

Tainan

Yunnan (a province of China) / a place name, such as that of Un'nan City in Shimane Prefecture

Haenam (a county of South Jeolla, South Korea)

Hainan (an island in the South China Sea) / Hainan (a province of China) / Hainan (a district of Wuhai, Inner Mongolia, China) / Kainan (a city in Wakayama Prefecture)

Alternative form of 鳦 or 乙: swallow