Synonyms for Impermanent (same or very similar meaning)
WordNet sense 1 (tending to vanish like vapor):
evanescentWordNet sense 2 (lasting a very short time):
ephemeral, passing, transientWordNet sense 3 (not permanent; not lasting):
temporaryWordNet sense 4 (bounded or limited in magnitude or spatial or temporal extent):
finiteFrom the ODE community, based on WordNetadd/edit