innermost thoughts; deepest feelings
A literary, somewhat old-fashioned word for what one truly thinks or feels deep inside. Often used in expressions like 胸臆を打ち明ける or 胸臆に秘める.
He finally revealed his innermost thoughts.
The letter was filled with her deepest feelings.
Compound of 胸 (chest, heart) and 臆 (innermost thoughts, feelings). The exact historical derivation is uncertain; the spelling is conventionally associated with deep, hidden emotions.