Unbelief = lack of faith, state of not believing in God, religion.
- Living in an age of unbelief.
- He is in the darkness of unbelief.
Unbeliever = Person who doesn’t believe in God, religion, etc.
Disbelief = inability or refusal to accept that something is true or real; scepticism, doubt, amazement, astonishment.
- They stared at the Taj Mahal in disbelief.
- The world reacted with disbelief to the news of his death.
- She shook her head in disbelief.
- Her first reaction to winning the award was disbelief.