Because/bɪˈkəz,bɪˈkɔːz/ Definition 1 of 4Pro Tip 1/2Expressing Reason Use 'because' to clearly explain the reason behind someone's action or a situation. She smiled because she felt happy. Pro Tip 2/2Cause and Effect 'Because' links the cause of an event directly to its effect, indicating a clear relationship. We left early because the weather was getting worse.