First off, I'm not referring to malapropism.
I've heard and read a word used before to describe a word in which it is in the situation of being misused; The public thinks it has one meaning, and now this meaning has become the accepted meaning (by the public), thus it is misused in a all the time, when in reality, that meaning is incorrect.
The situation in which I first heard this word used was the GNU/Linux naming controversy. People often use the term "Linux" to mean an actual operating system or refer to the combination of GNU userland with the Linux kernel, when in reality (textbook definition, I guess) it's a kernel, but since it is so widespread, calling it GNU/Linux or something else would be strange to some people.
If it helps, I believe the word started with a 's'.(Maybe not, but I could have swore it started with s....)
Edit: I believe the word I was looking for was metonymy. I suppose my placement of stress on the fact that the use of the word is a misuse, when for a metonymy, it doesn't neceassrily have to be (I believe), might have misled some of you. I'm not sure if metonymy is the word, but I'll look a little bit more before accepting the answer.