late 13c. as a form of address, 1570s as a synonym for "loved one;" from sweet (adj.) + heart (n.). As an adjective, with reference to labor contracts, it is attested from 1959.
he's a sweetheart
another sweetheart deal based on political influence
sweetbread
sweet-briar
sweeten
sweetener
sweet-grass
sweetheart
sweetie
sweetly
sweetmeat
sweetness
sweet-pea
