look up any word, like fleek:
 
1.
Someone who was raised with religion but later abandoned the practice.
"Are you an atheist?" "Nah, but I was raised a Catholic. I stopped practicing years ago. I guess you could call me an extheist."
by Philosophistry February 25, 2009
 
2.
Someone who formerly was a theist, believing in God and/or gods, or other supreme being, but who has given that belief up, becoming either an agnostic or an atheist.
I used to believe in God, I was a full-blown theist, but now i've rejected that, i'm an extheist if you will.
by Man from Another Place April 09, 2009