знать

very common #40A2

verbimperfective perfective is узна́ть

1.
to know, to be aware, to know about
Я не зна́ю, где он живёт.
I don't know where he lives.
Used with facts, clauses and о + prepositional; дать знать = to let (someone) know.
2.
to know (a person), to be acquainted with
Я хорошо́ зна́ю его бра́та.
I know his brother well.
With a direct object denoting a person, place or thing one is familiar with.
3.
to know (a subject), to have a command of, to be good at
Она́ зна́ет три языка́.
She knows three languages.
Of languages, subjects, one's job.
4.
(rare) to seem (apparently, evidently)
Знать, дождя́ сего́дня не бу́дет.
Apparently it's not going to rain today.
Colloquial, folksy; used as a parenthetical word, often with видно.

Examples

Я зна́ю только э́то.
I know only this.
Я не зна́ю, где э́то.
I don't know where it is.
Я не зна́ю, откуда тако́й слух.
I don't know the origin of the rumor.
Я зна́ю твоё и́мя.
I know your name.
Как вы уже зна́ете.
As you already know.
Совсем не зна́ю.
I don't have a clue.
Я не зна́ю, как показа́ть э́то, поскольку э́то и так вполне ясно.
I don't know how to demonstrate it, since it's too obvious!
Вы зна́ете ра́зницу между микроско́пом и телеско́пом?
Do you know the difference between a microscope and a telescope?

Imperative
ты	зна́й
вы	зна́йте

Active present	зна́ющий	learned, scholarly, erudite, skilful
Active past	зна́вший	who knew, having known, acquainted with
Passive present	зна́емый	known, familiar
Passive past	знанный	known, well-known, famous
Gerund present	зна́я	while doing (present)
Gerund past	зна́в знавши	while doing (past)

LockedUnlock typical usages

Verb	Prefix	Meaning
знать	-	to know; to know (a person); to know (a subject); to seem (apparently, evidently)
зна́ться	-	to associate
вы́знать	вы-	to fully know
позна́ть	по-	to get to know; to experience