heart-root
/ˈhɑːtruːt/(also heart's root)
noun
1The source of a person's most profound emotions; the bottom of the heart. Also in plural in same sense. Compare heart, root. Now poetic and rare.
2A large, obliquely descending tree root, as contrasted with a vertical taproot or a horizontal root. Frequently attributive, especially in heart-root system.
Origin
Middle English; earliest use found in Trinity Cambridge Manuscript. From heart + root. In some forms probably originally reflecting a genitive compound with unmarked first element. In some forms from the genitive of heart + root.