sweetheart
n. countable B1 Intermediate US //ˈswitˌhɑɹt// UK //swˈiːthɑːt// sweet·heart
n. a kind person or someone you love very much. You can use it as a name for a romantic partner or a close friend.
n. a person for whom one has romantic feelings, or an individual regarded as exceptionally kind or generous. Often used as a term of endearment in direct address.
She is such a sweetheart for helping me move.
The elderly couple had been sweethearts since they met in high school sixty years ago.
From Middle English swete heorte, swete hert (term of endearment); equivalent to sweet + heart.
Usage
Commonly used as a vocative (a word used to address someone directly).