sincere, faithful
訦 centers on sincerity and faithfulness in speech or character: being honest, trustworthy, and true to one's word.
訦 combines 言 (speech) with 冘, which likely contributes the sound and may relate to sincerity or trustworthiness. The exact historical development is uncertain.
Words (言) that are sincere and faithful come from a deep, steady place, like the stable shape of 冘. Picture honest speech flowing from a calm, unwavering source.
For シン, imagine a sincere person speaking from the heart: their words are a true 'shin' (シン) of light, like a pure, faithful beam.