whispering; quiet weeping
Refers to a low, subdued sound made while trying not to be heard, such as a whisper or muffled sobbing. Often used in literary or poetic contexts.
I heard a quiet weeping sound in the middle of the night and thought someone was crying.
She revealed the secret in a whisper.
Compound of 忍び (stealth, concealment) and 音 (sound). The exact historical derivation is uncertain, but the word is conventionally associated with sounds made while trying to avoid detection.