This is the 3rd most frequent Estonian word.
ka
"Ka" in Estonian means "also" or "too."
In this sentence, 'ka' is used as 'also' to emphasize that the book is not only interesting but has the additional quality of being educational.
See on huvitav raamat, ka väga õpetlik.
This is an interesting book, also very educational.
Here, 'ka' means 'as well,' implying an inclusion to an ongoing invitation where others may already be included.
Kas sa tuled ka peole?
Will you come to the party as well?
In this sentence, 'ka' is used to mean 'also,' indicating an additional element in the list of things I eat.