The term underpinned implies a support or foundation for something. The antonym for underpinned is unstable, which means uncertain or unreliable. Something that is not underpinned lacks a firm and sturdy foundation, and it can be shaky, wobbly, or flimsy. The opposite of underpinned can also be precarious, which refers to something that is unstable, dangerous, or risky. While underpinned indicates a sense of security and stability, its antonyms suggest the opposite, and they highlight the importance of having a strong foundation to maintain equilibrium and prevent potential collapse.