the name of the letter (jamo) ㅇ of the hangeul writing system
Etymology
Coined at 1527 as 異凝 in Hunmongjahoe (訓蒙字會, Introductions of the Letters for Youth), written by the court interpreter Choe Sejin. Originally it was the name for obsolete consonant ㆁ(ng), which is now lost its sound at initial and replaced by consonant ㅇ, which originally referred no sound at initial and was named 이(伊) on same book. Each Sino-korean letter is used only for showing Korean pronunciation, as Sino-korean 異 has the initial ㅇ in its pronunciation, and 凝 has the final ㅇ.