depths; inner mysteries; heart
Refers to the profound, hidden essence of an art, discipline, or one's mind. Often used in literary or philosophical contexts.
He trained for many years to master the depths of the tea ceremony.
That philosophy book delves into the inner mysteries of the human mind.
Describes something as deeply meaningful, abstruse, or not easily understood. Used as a な-adjective.
His lecture was profound and difficult for beginners.
This scripture contains esoteric teachings.