heart of hearts

Noun

heart of hearts (plural hearts of hearts)

1. (idiomatic) One's innermost private feelings.
   • Yet the darling sin is there in our heart of hearts; we hug it close—we hide it from every human eye. But in the still night-watches it comes forth like a serpent out of his hole, and rears its venomous crest, and stings us with the horror of our guilt.1876, [Mary Elizabeth Braddon], “At His Door”, in Joshua Haggard’s Daughter […], volume III, London: John Maxwell and Co. […], →OCLC, pages 180–181
   • With the "Constance," which in his heart of hearts he loathed, departed the last remnant of Cheyne's millionairedom, and he gave himself up to an energetic idleness.1896 November – 1897 May, Rudyard Kipling, chapter X, in “Captains Courageous”, Garden City, N.Y.: Doubleday & Company, published 1897, →OCLC