Hangul syllable senh

On its own, 섾 is a syllable, not a complete word. It combines ㅅ as the initial consonant, ㅔ as the vowel, and ㄶ as its final consonant cluster. It can sit inside a Korean word, where the surrounding syllables supply the meaning. The label senh identifies the syllable; it does not translate it. The final ㄶ is a compound ending consonant group, and its sound in a Korean word can depend on the next sound.

Hangul was made to write Korean speech with consonants and vowels arranged into syllable blocks. Its first record is dated 1443; the book Hunminjeongeum, which explains the system, was published in 1446. Older Korean texts can reflect pre-1933 spelling conventions. Unicode can represent a modern syllable as one precomposed block or as a sequence of Jamo, the consonant and vowel letters used to build Hangul syllables.

Why does 섾 split into separate letters?

It may be one block or a sequence of Jamo. Unicode represents the syllable both as precomposed 섾 and as the conjoining-Jamo sequence 섾. NFC combines that modern consonant-vowel-final sequence into one syllable; NFD separates it. A font and app need to shape the separated letters properly for them to appear as one Hangul block.

With a Korean IME, enter ㅅ, then ㅔ, then final ㄶ (ㄴ + ㅎ); the IME assembles the block. For software that needs one precomposed character, normalize the sequence to NFC.