Formal:
* प्रिय (priya): This means "dear" or "beloved" and is a very formal and respectful term.
* मनमोहक (manmohak): This means "enchanting" or "captivating" and can be used for someone you find very attractive.
Informal:
* जानू (jaanu): This is a very affectionate and playful term, similar to "honey" or "sweetheart" in English.
* प्यार (pyaar): This means "love" but can also be used as a term of endearment.
* आशिक (ashiq): This means "lover" and is a more poetic term.
* मेरे दिल का टुकड़ा (mere dil ka tukda): This means "piece of my heart" and is a very loving and intimate term.
The best translation for "sweetheart" in Hindi will depend on the context and the relationship you have with the person you are addressing.