This is an idiom of affection. They are not actually brother and sister. See how you translated this in [Song of Songs 4:9](./08.md). Alternate translation: "my dear" or "my darling" (See: [[rc://en/ta/man/translate/figs-idiom]])
This Hebrew word can refer to a woman who is married or to one whom a man has arranged to become his son's wife. If your language has a polite word that a man would use to his wife and that has not been used yet in this book, you could use it here. Otherwise you could use any polite term a man would use with his wife. See how you translated this in [Song of Songs 4:9](./08.md).
The verb may be supplied from the previous phrase. Alternate translation: "how much better is the fragrance of your perfume than the fragrance of any spice" (See: [[rc://en/ta/man/translate/figs-ellipsis]])