1. เจ้าหญิง (Chao Ying) - This is the most common and formal way to say "princess." It literally translates to "royal woman."
2. นางสาว (Nang Sao) - This is less formal and means "Miss." It can be used to refer to a princess, especially when talking about a younger princess.
Context is key! The choice of which term to use depends on the specific context and your level of formality.