All definitions in this come from the Merriam-Webster Online Dictionary. This is written using American figures because those are what I have researched.
edit Read this whole post before you post in this thread. If you do not, you did not get the point I was making and can go right back to tl;drville. By the end of this, you should NOT be commenting on the idea of homosexuality being a mental disorder. The chain of logic regarding that is put forward as a startling example of a greater truth about human discourse as is made perfectly clear at the end of this post. It was supposed to be a shock ending, but everyone is too fucking lazy to read it and get the full impact, so this warning became necessary.
This is not a discussion of homosexuality or of the word disorder by itself. It is a discussion of the way in which the language can be manipulated for control.
By definition, homosexuality could be described as a disorder, which is defined as "an abnormal physical or mental condition", condition simply meaning "a state of being" abnormal simply meaning, "deviating from the normal or average".
So, in essence, a disorder is "a physical or mental state of being that deviates from the normal or average state of being".
Now, average is defined as "not out of the ordinary" and ordinary is defined as "of a kind to be expected in the normal order of events".
Now, in my country, as of April 11th of this year, only 3.5% of the population is gay, lesbian, or bisexual.
http://wiwp.law.ucla.edu/wp-content/uploads/Gates-How-Many-People-LGBT-Apr-2011.pdf
You might argue that that is a large enough percentage to say that it is not something that could not be expected in the normal order of events. However, in such a case, I would have only one question for you: would you expect an "average" or "ordinary" American to support a shift to Communism? No sane person would answer yes, unless of course they thought the 3.5% could be considered ordinary, because a full 11% or Americans support a shift to Communism.
http://www.washingtonpost.com/blogs/the-fix/post/congress-approval-problem-in-one-chart/2011/11/15/gIQAkHmtON_blog.html#excerpt
Clearly, 3.5% is not enough to be considered ordinary. In this way, it is not average and meets our extended disorder definition "a physical or mental state of being that deviates from the normal or average state of being".
So, where am I going with this? Well, I am not going to conclude that homosexuality is in any way wrong just because it can be considered a disorder. Nor am I honestly suggesting that homosexuality be considered a disorder. I am, instead, using this as a way to highlight a question as to how the fundamental building block of our interaction as humans, language, can be used to trick us into believing some rather horrendous things.
And this cannot just be applied to homosexuality. As a Communist, I see the threat of this sort of usage of the language, this totally technically logically sound use of the language I will add, to have my beliefs classified as a mental disorder. After all, only 11% of the population would support a shift to Communism while a full 16.6% of the population have a "Major Depressive Disorder".
http://www.mentalhealth.com/
"Of course a belief in Communism, being even more rare, is a disorder" they will say just as I have said to you "of course homosexuality, being so rare, is a disorder".
Most of us have read 1984 and we thought with horror about our language being stripped from us for control. However, such is unnecessary. The tools for atrocity are already present in the dictionaries and definitions we use every day to understand the world around us.
So, is homosexuality a disorder? No. Is being a Communist a mental disorder? No. Is being a Fascist or a Libertarian or any of those other unpopular states of being I disagree with a disorder? No.
However, they might be, if you trust Merriam-Webster or any other dictionary.
I suppose the point of all this is then, be careful out there, and don't let even the most beautiful wording and manipulation of fact persuade you to bigotry.