The Russian phrase for common sense is здравый смысл.

The primary meaning of виза is visa, the document without which you cannot enter a foreign country. The US and Russia have a tit-for-tat game going on that esentially means Russians can't come to the US without obtaining a visa (which is an onerous process), and Americans can't go to Russia without going through an annoying process as well. Here's a picture of my visa for the summer, with portions grayed out for obvious reasons. It occupies an entire page of my passport:

Back in the Soviet period a visa was a three-part form that was not attached to your passport. When you entered the country, they stamped the visa and removed on part. When you exited the country, they stamped and retained the rest of the visa so that once you were gone, there was no proof in your passport that you had ever been in the Soviet Union. I never quite figured out the reasons for that. Here's a photo of my visa from 1988:

Виза is a perfectly regular first declension noun:

Before you get a visa to Russia, you have to get an invitation from a family, hotel or business. That's a lengthy process as well. And of course there are fees involved. Once you get to Russia, you have to register your passport/visa with internal immigration, which produces another document and involves other fees. Then by law you are required to have your visa and passport and registration on you at all times, and the police can stop you at any time and demand to see those documents. And of course if you passport, visa or registration is stolen, then it's a major pain to get them replaced. And of course there are fees involved. It's entirely amazing how many problems can crop up with these things. For instance...

That may sound ridiculous, but it actually happened to one of my students in ’92. We were in Moscow at the time. Our visa support was in Leningrad. I ended up having to head back to Leningrad to get a new visa for him.

That also may sound ridiculous, but in fact that's what I had to pay for the visa for this summer.

That, too, may sound ridiculous, giving a complete stranger your passport, but in fact one of our students did precisely that in ’89. She got to know the American Embassy pretty well in the process of getting a new one.

That, too, may sound ridiculous, but all our students have to have HIV tests to get a visa. I think this is part of the tit-for-tat. Up until January of 2010 the US also required HIV tests for people getting visas to enter the country. Now that the requirement has been lifted, it will be interesting to see if Russia lifts it as well.

Most human languages have separate words for you-singular and you-plural. Russian is no exception. The plural you in Russian is вы, which declines like this:

Any time you address more than one person in Russian, you must use the вы form instead of the ты form:

In Russian the вы form is also used to speak politely to a single individual; it's the form you normally use when meeting a stranger or talking to someone who is your superior at work or to someone you don't know very well:

Now here is a subtlety. If вы is the subject of a sentence that has a predicate adjective, and if the adjective is a short form adjective, then you must use the plural form; but if it is a long form adjective, you must use the singular with corresponding gender agreement. Thus if I am talking to a woman I may say:

If I am talking to a man, I may say:

I should note that some of those sentences may sound a bit stilted in Russian. Russian-speakers tend to use predicate adjectives less often than English-speakers, and one needs a bit of experience to figure out when they sound okay and when one should use an alternative constructive. Grammatically, though, all four sentences are correct.

Okay, I lied on Friday. My favorite word in Russian is not слизь. It's слизняк. Слизь of course means mucous, and -няк is a suffix that forms a new noun, so слизняк is a ‘mucousling,’ in other words... a slug! Isn't that an awesome word?

Growing up in Tucson, Arizona, I never saw a live slug, so imagine my surprise when I moved to Seattle where they have banana slugs, which are bright yellow critters as long as a human arm!¹ Here's a picture:

Those -няк suffixes usually produce an end-stressed noun:

There is a more scientific version of this word as well, which is слизень. It is a soft masculine noun with a fleeting vowel:

Slugs are harmless unless you have a garden, in which case those slimy bastards will really piss you off:

You really should follow the link to that last one. The site has beautiful photographs...

¹ Well, as long as newborn's forearm... not an adult's arm.

One of the few Russian words that every American knows is космонавт, which of course is spelled ‘cosmonaut’ in English.¹ It is a perfectly regular noun that declines like this:

The космо- part is from Greek κόσμος, which meant universe (and nowadays ‘space’), and νάυτης sailor, thus a космонавт is a universe sailor, i.e., a space traveller. In English cosmonaut and astronaut are diffferent only in that the word cosmonaut applies to people of the former Soviet Union or of the countries that succeeded it. Astronaut is more general. It sounds perfectly normal to say “Yuri Gagarin was a Russian astronaut,” but to say “Alan Shephard was an American cosmonaut” sounds ironic.

In 1995 the French decided that astronaut was much too American a word to describe their own astronauts, so they coined the word spationaut. I'm rather amused at the attitude, particularly since the word astronautique was first used in French back in the 1920s, long before Americans decided on the word astronaut in the late 1959.² And then the Chinese, not to be outdone by the Americans, the Russians and the French, decided they needed their own word as well, so in 1998 the word taikonaut was coined from the Cantonese word taikong ‘space’ to refer to Chinese astronauts.³

Whew, can political correctness get much correcter? Now I have to distinguish cosmonauts from taikonauts from astronauts. And with great glee I can now call French astronauts “spacey-o-nauts.”⁴

¹ The other two Russian words every American knows are vodka and czar.

² See an interesting discussion of the orgin of the word on http://www.collectspace.com/.

³ For commentary on the usage of the word taikonaut see this Wikipedia article.

⁴ Note to Russian speakers: in colloquial American English ‘spacey’ means ‘inattentive’ or ‘irresponsible,’ so spationaut when deliberately mispronounced as spacey-o-naut sounds mildly derisive and may evoke a chuckle from American listeners.