divulge, reveal
訐 centers on making something known that was hidden: divulging secrets or revealing private information, often with a sense of exposure.
訐 combines 言 (speech) with 干, which likely contributes the sound and may suggest exposing or laying open. The exact historical role of 干 is uncertain.
Words 言 beside a shield 干: imagine someone lowering their shield and letting words spill out, revealing hidden truths.
For ケツ, picture a kettle of secrets boiling over and divulging steam: kettle -> ケツ, and the words escape like steam.