It is worth pointing out, before embarking on the mission of tracking down the most misused word in the English language, that usage is an evolving trait of any language and that the "misuse" of certain words today will likely be an essential element of the language tomorrow. This is part of what makes learning a foreign language difficult and part of the reason why, despite their best efforts, language academics remain largely unable to control what words and expressions come to signify to the general public.
Upon being asked what the most misused word in English is as of right now, most peoples' first instinct is to blurt out the most overused word they can think of, i.e. "like," "really," "actually," etc. While these words are definitely used in a way not accepted by most people as being "correct" (especially in the case of "like"), and while an easy argument could be made for them being the most frequently botched words in the language, these are not what come to mind when I think of the "most misused."
The word "misuse" itself is generally defined as either improper use or abuse of some kind. Without doubt the vast majority of us improperly use the language every day, including those of us who actually know what we are doing when it comes to putting together a sentence. We simply can't be bothered, and perhaps shouldn't be, to consider how we sound when the important thing is getting our meaning across. The corporate world has also destroyed much of our need for specificity as we strive to create a language friendly enough to accommodate everyone without delay, to make us all feel as though we are on the same page. Such an observation leads us much closer to the doorstep of the worst kind of language misuse, but does not quite get us inside.
To me "misuse," regardless of its various possible meanings, connotes, at its peak (which is what we are, I presume, talking about here), blatant improper usage. I also feel that we must be talking about a word that has snuck into misuse so cunningly that most people don't even realize it and therefore don't think to correct themselves. This is not to say that peoples' ignorance is a direct factor in the word being misused, as misuse can occur just as thoroughly if someone is entirely aware of it, but that for a word to be misused on the kind of scale which we seem to be considering, I suspect ignorance must be key.
That said, the most misused word I can think of is "freedom," and by proxy the word "liberty." Along with these comes more rhetorical weight than the average person can bear. In the Western world, we have the aforementioned terms thrown at us by politicians who do not bother to explain them but expect us to fill in the blanks ourselves, or rather be filled with the shame of not knowing. To use the most obvious example, someone can say that they are all for bringing "freedom" to the people of Iraq, meaning that they back the President of the United States and his "mission" to "free" Iraq. In doing so they make the glib presumption that
the free market + representative democracy + nation building = freedom
and that anyone who is against any of these things is against "freedom." Those who disagree may then argue in response that freedom is something different, that freedom is about personal choice, that it is about social welfare, that it is about a woman's body or a cluster of cells, and in doing so will contribute to the misuse of the word. Therefore all these situations which merit discussion on their own terms become simply about ownership of a single word. We have made much of the way we understand the world about a combination of sounds we don't even bother to explain to ourselves much of the time.
The degradation and misuse of this word has nothing to do with my own political views, or anyone else's, for that matter. The problem is that "freedom" is by nature, by connotation, and even, I would argue, by definition, a word that requires a qualifier. Like "God," it is not something we can throw around as an absolute value while still expecting to understand one another. To speak of "freedom of speech," or "separation of church and state," or "limited government" is to open conversation on specific topics which can be challenged by detailed discussion. This is, I think, how we should speak of freedom.
My copy of Webster's gives no less than seventeen definitions. Is this something we can afford to be unclear about? I think it is fair to say that such a word needs explanation for proper usage. Not bothering to provide explanation or qualification should count not only as improper usage but as outright abuse of the language. This is not casual modification or even a matter of dressed-up corporate fetishism. True misuse is not about language purity, as I see it, but a matter of basic decency. Language by itself is nothing sacred. The fact that "hopefully" was once a garden-variety adverb but can now be used at the beginning of sentences to express intention or emotional value is nothing to sob over. People in the United States and the world over have laughed at President Bush's pronunciation of the word "nuclear," but have probably done so in order to distract themselves from his more serious abuses of English as a mode of communication. It is easy to be duped by social prodding if we do not admit that our understanding of words changes over time and differs from person to person. We ought to be wary of pretending that respect for the language involves shutting out that realization when it should, in fact, reflect it.