Formal:
* สวัสดี (Sa-wat-dee) - This is the most common and polite way to say hello. It can be used in almost any situation.
* สวัสดีครับ (Sa-wat-dee khrap) - This is the formal way to say hello for men.
* สวัสดีค่ะ (Sa-wat-dee kha) - This is the formal way to say hello for women.
Informal:
* หวัดดี (Wat-dee) - This is a more casual way to say hello, used among friends and family.
Other ways to greet someone:
* สบายดีไหม (Sa-bai-dee mai) - This translates to "Are you well?" and is a common way to greet someone.
* อรุณสวัสดิ์ (A-roon sa-wat-dee) - This means "Good morning" and is used in the morning.
* สวัสดีตอนเย็น (Sa-wat-dee dorn yen) - This means "Good evening" and is used in the evening.
* ราตรีสวัสดิ์ (Ra-tri sa-wat-dee) - This means "Good night" and is used at night.
Remember to use the appropriate greeting depending on the situation and who you are talking to.