used to represent sound
吚 is a rare kanji used to represent a sound, likely an onomatopoeic or mimetic expression. Its standalone meaning is unclear beyond this sound-representation function.
吚 combines 口 (mouth) with 尹, likely as a phono-semantic compound where 尹 contributes the sound and 口 indicates a vocal expression. The exact historical development is uncertain.
The mouth radical 口 beside 尹 suggests a sound coming from the mouth. Picture a mouth making a distinctive 'ee' sound.
For イ, imagine the mouth 口 making a long 'eee' sound: ee -> イ, like a sustained note.