sweet·heart / ˈswētˌhärt/ • n. used as a term of endearment or affectionate form of address: don't worry, sweetheart, I've got it all worked out. ∎ a person that one is in love with: the pair were childhood sweethearts. ∎ a particularly lovable or pleasing person or thing: he is an absolute sweetheart. ∎ [as adj.] inf. denoting an arrangement reached privately by two sides, esp. an employer and a labor union, in their own interests: a sweetheart agreement.