Believe/bɪˈliːv/ Definition 1 of 5Pro Tip 1/2Real or Imagined Use 'believe' when you're unsure if something is true, but you accept it could be. I believe there's life on other planets. Pro Tip 2/2Evidence-based Belief When you think information is credible based on some evidence, you 'believe' it. I believe her story; the facts check out.