Refuse
Definition 1 of 3
Pro Tip 1/3
Strong Denial
Used to firmly reject something, often with determination. He refused the offer with a shake of his head.
Pro Tip 2/3
No Negotiation
Implies a non-negotiable stance when declining something. She refused to negotiate on the price.
Pro Tip 3/3
Polite Disagreement
Can be used politely in social contexts to decline offers. I must refuse your invitation, but thank you.