Hangul Letter Kapyeounpieup

It is an obsolete Middle Korean letter for a voiced lip sound. It marked a voiced bilabial fricative, usually reconstructed as [β]: the lips come close while voiced air passes through. The broad sound description is accepted, though its precise historical pronunciation remains debated.

ㅸ belongs to the fifteenth-century Hangul tradition. The Hunminjeongeum, a manuscript introducing and explaining the Korean alphabet, was published in 1446. This is an old writing-system letter, not a modern invention; Modern Korean no longer uses it as a separate consonant.

What happened to ㅸ?

Many forms shifted toward w, while the separate sound faded. The letter survived into the 1450s; in many words its sound changed toward w, while some recorded forms developed an i sound. The modern form of a word can preserve that history even when the old letter is gone.

The alternation helps explain pairs such as 덥게 and 더워: the older light-labial sound helps account for the w in the modern form. Read ㅸ as evidence of an earlier Korean sound system, not as a guide to pronouncing modern Korean.

How is ㅸ related to ㅂ?

It is historically related to ㅂ, but marked a different sound. In the old yeonseo convention, a labial letter was joined with ㅇ to mark a “light” labial sound. The related set includes ㅱ, ㅸ, ㆄ, and ㅹ.

Its historical position also matters: descriptions place ㅸ between vowels, in y–V and r–V environments (V means a vowel), and in a separate setting related to ㅍ. The associated archaic choseong form is ᄫ; it is a related Hangul form, though fonts may draw it differently.