Why Define?

I define nothing. 

Definitions of words come from the revelation of God to Adam, the forefathers and mothers, Moses, then the chain of prophecy. 

For Jews, prophecy stopped with Malachi. For the children of Noah, as long as a prophet does not contradict the word of God, he may be a true prophet/messenger for the people he or she was chosen to communicate the will of the Lord to. Definitions of words also spring from cultural progress. The word "mind" used to connote "listen to". Now it connotes "not bothered by". 

Language changes, but slowly and not through force, that is, not through forced speech and fines or jail time. Regarding the chain of prophetic tradition, it may be a good exercise to look at scripture and tradition and see, what have Judaism, Christianity, and Islam meant when they referred to men and women? 

There is a legal side and a philosophical side to Abrahamic religions. In Judaism, a man divorces a woman by handing her a document of divorce. Can this process happen between two women? 

Between two people who will not say what gender they are? The terms "man" and "woman" must be defined in order to function in an orderly society. There is also a philosophical side to monotheistic religions. Dina is the only example I can think of a woman who is considered by Jewish tradition to have had manly charactaristics. She is the foremother of the tribes Efrayim and Menashe. She birthed a daughter, Osnat, who married Josef when he was viceroy in Egypt. A tomboy is not necessarily a trans person. 

Jewish tradition is not flooded with overwhelming examples of transgender people. You can philosophize here and there about what it means to be effeminate and tomboyish, that is a wonderful exercise. But that cannot blur the importance of the following: where do definitions of words come from, and why do we need to define them? I wish you blessings on your journey.