This is the 58th most frequent Indonesian word.
kembali
"Return" or "you're welcome" (context-dependent).
'Kembali' is used here to mean 'return' or 'come back' indicating movement back to a previous location.
Saya kembali dari liburan kemarin.
I returned from the vacation yesterday.
In this sentence, 'kembalikan' (derived from 'kembali') means 'return' as in giving something back to its original place.
Tolong kembalikan buku ini ke perpustakaan.
Please return this book to the library.
'Kembali' here is an idiomatic expression used in response to thanks, equivalent to 'you're welcome' in English.