This is the 113th most frequent Czech word.
od
"Od" in Czech means "from" or "since."
In this sentence, 'od' is used to indicate origin, specifying the source of the book.
Kniha je od mého bratra.
The book is from my brother.
Here, 'od' is utilized to indicate the starting point in terms of time, showing when he started being there.
Byl tam od rána do večera.
He was there from morning till evening.
In this context, 'od' denotes the sender or the origin of the letter, identifying it as being from the government.