The crossword solution for the term 'heart or soul' is PITH, which is a four-letter word. PITH is defined as the essential part of something, or the core of an idea or emotion. It is often used to refer to the innermost part of a plant stem, or the soft tissue in the center of a stem. In terms of emotions, it can be used to describe the essence of a feeling or thought. PITH can also be used to refer to the innermost part of a person's character, or the core of their being.