Under-propped is a term used to describe something that is not properly supported or lacking proper reinforcement. Synonyms for this term include under-supported, poorly reinforced, weakly held, insufficiently braced, inadequately bolstered, and feebly buttressed. Other similar words that can be used include unsustained, unstable, flimsy, rickety, fragile, and unsteady. These words describe a situation where the support given to something is not adequate, and therefore, the object may be at risk of collapsing or giving way. When describing something as under-propped, these synonyms can be used to convey the sense of instability or lack of strength in the object.