The word "un-believing" refers to a lack of faith, trust, or acceptance of something. Its antonyms, on the other hand, denotes strong convictions and beliefs. Some of the antonyms for un-believing are credulous, faithful, trustful, trusting, gullible, and naive. These words express a sense of confidence, assurance, and conviction in one's beliefs or values, indicating a strong faith or allegiance in something or someone. Having a positive belief system and trusting in the world around us can be beneficial in building solid relationships and a sense of security and stability in life.