The adjective “sweet” refers to something sweet-tasting, but it can also be written as a noun — an affectionate term of endearment spelled “sweetie” or “sweety.” The word is most commonly spelled with an “ie” rather than a “y,” though both are considered correct.

a very pleasant or kind person: He's a real sweetie. [ S ] informal used for talking to someone you love, such as a child, partner, or good friend: [ as form of address ] It's time for bed, sweetie.

used for talking to someone you love, such as a child, partner, or good friend: [ as form of address ] It's time for bed, sweetie.