This is the first word that we will greet each other. It might also be the first Thai word that you know but it’s not Thai. Actually, this is a Sanskrit word, created by Phraya Upakitsinlapasan (1879 – 1941) for greeting between students and professors in the faculty of Liberal Arts, Chulalongkorn University when he worked as a professor there. It became official greeting word in 1943 by Field Marshal Plaek Phibunsongkhram (1897 – 1964), the Prime Minister of Thailand at that time.
สวัสดี /sà-wàd-dēe/ coming from a prefix สุ /sù/, meaning good, beautiful, easy and a word อสฺติ /àd-sà-dtì/, meaning there is, there are, have. When these two words merged together following the grammar rules, สุ /sù/ became สว /sà-wà/. Plusing อสฺติ /àd-sà-dtì/, สวสฺติ /sà-wàd-dì/ means ‘Wish (you) goodness and virtue!’ Actually, it reminds me of the phrase “May the force be with you!” Ring a bell? Lol
This word originally is short vowel sound for all syllables but Phraya Upakitsinlapasan changed the last syllable into a long sound to make it sounds better.
After that, there were some more greeting words created such as อรุณสวัสดิ์ /à-run-sà-wàd/ for ‘good morning’, ทิวาสวัสดิ์ /tí-waa-sà-wàd/ for ‘good afternoon’, สายัณห์สวัสดิ์ /săa-yan-sà-wàd/ for ‘good evening’ and ราตรีสวัสดิ์ /raa-dtee-sà-wàd/ for ‘good night’. However, these words are not as popular as สวัสดี /sà-wàd-dēe/ which we can use any time during the day. Only อรุณสวัสดิ์ /à-run-sà-wàd/ for ‘good morning’ and ราตรีสวัสดิ์ /raa-dtee-sà-wàd/ for ‘good night’ that people still use until now.
May the virtue be with you!