The word gender comes from the Latin word genus, meaning kind, type or sort. Its original use was for grammatical categories, and it was not used as an identifier of human nature until the mid 20th century. In fact it wasn't until the feminist movement of the 1970's that it became more or less synonymous with the word sex. When applied to the human condition, it is purely abstract, and as such is highly subjective. There is no way to provide a finite definition of what constitutes gender and even less of a way to define its individual components of masculinity and femininity. They mean whatever you want them to mean.
Any meaning that can be attributed to the word transgender, is totally dependant upon the meaning one gives to the word gender. When you use it as an adjective to describe an individual, you are using a descriptive adjective which provides the complete description of a certain aspect of that individual; namely his identity with regard to his gender. It is like saying his eyes are blue or his race is Caucasian. It does not change from time to time, but is a constant. The gender feelings might be fluid, but he is by strict definition and grammatical logic always transgender.
Cross gender expression is an equally ambiguous term because it is still dependant upon the meaning of the word gender. It is also dependant on the meaning of the word expression. Clothing is just a small component of expression. We have to look at behaviour, activities, interests, instincts, and more to have a more complete picture of expression. Is a man who is feeding a bottle to his infant child in the middle of busy mall indulging in cross gender expression? What if he was wearing skirt? Where does it begin and where does it end?
I do not agree with the way the term transgender is used by the media, nor do I agree with the conflating of sex and gender, which is just one more reason why I reject the current usage of these terms. Others may feel comfortable using this gender related terminology, but I don't. I object to its use as an umbrella term as it is extremely misleading, is open to many false stereotypes and imposes the above mentioned complete description of what I am.
I do not think that crossdressing is the greatest term in the world, but it is descriptive, does not peg me as being anything other than someone who indulges in a certain activity, and can be used as an adjective, verb and noun, just like golf, swim or walk.
I am not aware of any classic sense of crossdressing. Wearing a single item of underwear could be construed as crossdressing, depending upon motivation. Similarly, dressing to the nines, complete with makeup, forms, wig and jewelry is also crossdressing according to he basic definition of the word, which is the wearing of clothing intended for the opposite sex. Why does it have to represent the expressing of anything more than the love of the thrill of being adventurous, or daring or curious?
Veronica