The term 'at heart' is used to describe someone's true nature or character, and the crossword solutions for this term reflect this idea. FUNDAMENTALLY (13 letters) suggests that the person's true nature is rooted in their core beliefs and values. Inesse (6 letters) implies that the person's true nature is inherent and intrinsic. Atbottom (8 letters) and bynature (8 letters) both suggest that the person's true nature is fundamental and inherent. Deepdown (8 letters) and INNATELY (8 letters) imply that the person's true nature is deeply rooted and instinctive. Finally, BASICALLY (9 letters) and inessence (9 letters) both suggest that the person's true nature is essential and basic.