여든
yeodeun · TOPIK 1
eighty
여든 (80) echoes 여덟 (8): same yeod- start, plus the tens ending -eun
Native Korean tens often reuse the unit's opening sound: 여덟 (yeodeol, eight) becomes 여든 (yeodeun, eighty). The -eun/-heun ending also shows up in 일흔 (seventy) and 아흔 (ninety), so yeod- + -eun = eight-ty.