Yeorinhieut

Yeorinhieut is an archaic consonant letter of the Korean alphabet, Hangul. In Unicode, its name is spelled yeorinhieuh, following the ISO/TR 11941 romanization system. It was historically widely called doenieung, but the South Korean National Institute of Korean Language decided in 1991 to officially name it yeorinhieut because it was felt that contemporary South Koreans would more visually associate the graph with hieut over ieung. It was associated with a glottal stop.
It has a stroke added from ㅇ; the Hunminjeongeum Haerye, the text that introduced Hangul, introduces the two characters as having similar sounds, and when transcribing Korean it says they can be used interchangeably. Various scholars argue that ㆆ was relatively artificial and mostly used as an initial consonants for Sino-Korean words in Chinese dictionaries that begin with a glottal stop and was otherwise not used much. For Korean, it could be used to indicate preglottalization before a tensed consonant. It largely fell out of use by the end of the 15th century, after which its role was replaced by ㅅ.