I apologise for appearing harsh, I'm just being honest...
Addison became a female name because 1. people became tired of
Madison, and 2.
Grey's Anatomy became popular around the same time, and gave people the idea that
Addison might be a good substitute. While a fictional doctor on soap opera-ish medical drama is perhaps a better namesake than a fictional mermaid who took her name from a random street sign, I just don't get why people think a name meaning "
son of Adam" is etymologically appropriate for a girl.
Alison is tons better, and because of its medieval source, lasting popularity, and legit feminine meaning is far, far less trendy and dated than
Addison or any other "son of" names for girls. I can guarantee you that in 50 years
Alison won't be thought of as we think of
Bertha or
Gertrude today, like
Addison on a girl will be.
Changing the spelling doesn't change the meaning, and it certainly doesn't make a male name feminine. Changing the spelling only results in the name looking trendier and more illiterate to me. The Magycal Randym Y is, in fact, not magical.
Now,
Addison for a boy is a different story. It's still trendy, but etymologically it's appropriate for a boy, and for some reason to me it projects a bit of a Victorian aura. And if the
Addison in question is actually a son of an
Adam, or if
Addison is Mom's maiden name, so much the better!
For a girl, you could have several choices, all of which are genuinely feminine to me:
AdelineAdelinaAdelaAdele / Adèle
Adelyn (admittedly trendy and made up, but I could grudgingly accept it as a new creation made
a la Madeline ->
Madelyn)
AdaminaMadelineMadelyn