This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
讔 combines 言 (speech) with 隱 (hidden, obscure), suggesting a hidden or obscure meaning in speech. The exact historical development is uncertain.
The speech radical 言 beside the hidden/obscure component 隱 suggests a hidden meaning or riddle. Picture a secret message hidden within words.
For イン, imagine an inn where people whisper hidden riddles: inn -> イン, and the hidden speech fills the room.