The word 're-gaining' suggests the process of recovering or retrieving something that was lost or taken away. Some antonyms for 're-gaining' could include: losing, reducing, decreasing, surrendering, or forfeiting. Losing implies the opposite of gaining, meaning to misplace or have something taken away. Reducing and decreasing refer to making something smaller, implying that instead of gaining, something is being diminished. Surrendering and forfeiting both suggest willingly giving up or abandoning something, further contradicting the idea of 're-gaining'. Overall, these antonyms represent the opposite of regaining and highlight the potential loss or absence of what was once gained.