Metastable is a word used to describe a state of matter that is not quite stable, but not quite unstable either. It sits in a sort of limbo where it could shift into a more stable state, but hasn't yet. For this reason, there are a few synonyms that can be used to describe this state. These include "unstable equilibrium," "transiently stable," "precarious stability," and "labile." Each of these words underscores the idea that something is not fully stable, but instead in a state of flux where it could move in one direction or another. Overall, these synonyms help to paint a picture of a system that is always on the brink of change.