The opposite of faith would have to be both: hating & rejecting God
I think doubt as an opposite would diminish what we mean by faith to an extent like how London said.
Saving faith in Christianity is a:
1) Turning away from our natural desires or you could say repenting from self reliance (usually self) because we recognize that “every intention of the thoughts of our heart is only evil continually” Genesis 6:5 the human race is inherently evil yet we love ourselves but repentance begins with a low view of self & a hatred of your sin Matthew 5:3
2) Trusting Jesus & his desires (a trusting faith). This is literally removing yourself (or your idol) from being lord of your life & involves relying on God in everything who is perfect to begin with.
I think an antitheses would be turning away from God, hating who he is (he’s supposed to be your God), and trusting in who you are and your way, loving your own sin while considering what’s actually good to be evil.
Self reliance is opposed to faith, but if you get to the bottom line hating & rejecting God is the opposite of faith (loving and trusting him) opposed to sin. I go past self reliance because some people are more consumed with other creatures like another sinner or idols of a false religion… thoughts?
What Does It Mean to Believe? http://www.ligonier.org/blog/what-faith/