Hangul Choseong Sios-Pieup

It is a historical Hangul cluster at the start of a syllable.

Hangul syllable blocks start with a consonant and a vowel, sometimes followed by another consonant. Here the beginning combines two Hangul letters, ᄉ (sios) and ᄇ (pieup), letting older spelling preserve a complex syllable start. Scholars disagree whether some early spellings represented two spoken consonants or marked a more tensely articulated consonant.

How did its spelling change over time?

Later spelling favored clusters beginning with ᄉ (sios).

The relevant spellings appear in Hangul texts from the fifteenth and sixteenth centuries. By the seventeenth century, spellings with a cluster like ᄲ competed with doubled-pieup spellings such as ᄈ. By the nineteenth century, complex initials were generally written as clusters beginning with ᄉ (sios). These forms are historically connected, but their spellings are not interchangeable.

How do I type old Hangul ᄲ?

Use an Old Hangul input method when one is available.

An ordinary Korean input method may not offer obsolete Jamo. A Jamo is an individual Hangul letter: follow ᄲ with a vowel Jamo to form a syllable block. Without archaic Hangul shaping support in the font and app, the sequence may remain separate.