Where does “இராத்திரி” come from?

இராத்திரி (Tamil) comes from Tamil ராத்திரி, from Sanskrit रात्रि, from Sanskrit रात्री, from Proto-Indo-Iranian HráHtriH, from Proto-Indo-European Hréh₁trih₂.

Ancestry of “இராத்திரி”, step by step

StepLanguageWordMeaning
1Tamilராத்திரிnight
2Sanskritरात्रिnight
3Sanskritरात्रीnight
4Proto-Indo-IranianHráHtriHstillness of night
5Proto-Indo-EuropeanHréh₁trih₂—
Every word from Proto-Indo-European Hréh₁trih₂ →Every word from Proto-Indo-Iranian HráHtriH →Every word from Sanskrit रात्री →