The word сон in Russian can be translated as ‘dream’ or ‘sleep’. It declines as such:

Russians are great believers in the predictive power of dreams. Almost every woman has a со́нник ‘dream interpretation book’ by her bedside so that she can consult it first thing when she wakes up. Sometimes my friend Евгений's mother dreams about cats, which she always takes as a sign that something bad is going to happen him, especially that some friend might stab him in the back, and she warns him to be careful and think twice about anything he does that day.

Dreams played a huge role in the prophecies of Ванга, a Bulgarian woman who predicted the future. She is kind of like a Slavic Nostradamus, and every Russian knows about her. You can read about her here.