There are so many examples of how words have changed over the years, going back hundreds of years. For example, the word "awful" used to mean "full of awe."  Words also change from one generation to the next.  There are many reasons for this, but slang and technology have certainly contributed to the process.

Slang, which used to be used mostly by younger people, to have a "language" of their own, has become more widespread among all generations, so that I sometimes hear things such as older people saying "Hey, dude." Words such as "gay," though, have completely entered the common language, with everyone now agreeing upon a new meaning, the word being used by politicians and newscasters, too.   The word now means "homosexual," although the word not all that long ago meant "happy" or "in a good mood."  In my own youth, people my age used the word "bad" to mean something very good, the complete opposite of its meaning. I occasionally hear younger people using the word this way now. 

Technology has brought us new uses for words as well. Today we have viruses that infect computers, not just people.  And a desktop is what we see when we turn on our computers, rather than the top of our actual desks.  The verb "hack" has changed meanings, too.  When we hacked at something, we were trying to cut it back, as we might hack away at a bush we wished to get rid of. Now it means unauthorized entry into a computer or network of computers.  Spam is another great example. Spam is a form of meat that comes in a can, in a sort of pasty consistency.  It is still sold in supermarkets. But now when we speak of spam, we are usually referring to those unwanted emails we get, the unsolicited ones that urge us to buy something or invest in some unsavory scheme in another country. 

I have included a link for you to some information about other words that have changed in meaning.  But if you listen carefully to those around you, particularly those of different generations, you will find some of these words yourself!