Under-pins refers to something that supports or strengthens a structure, object, or idea. The antonyms for under-pins would be words that describe weakening or causing something to become unstable. Some possible antonyms for under-pins may include terms like undermine, weaken, destabilize, impair, sabotage, or incapacitate. These words suggest the opposite effect of under-pinning and may indicate destructive or negative actions that lead to the collapse of a structure, system or concept. Understanding antonyms is important in communication as it helps to avoid confusion and ensures clarity of message.