Synonyms for Transient (same or very similar meaning)
WordNet sense 1 (lasting a very short time):
ephemeral, passing, short-lived, transitory, fugaciousWordNet sense 2 (not permanent; not lasting):
impermanent, temporaryWordNet sense 3 (of a mental act; causing effects outside the mind):
transeuntFrom the ODE community, based on WordNetadd/edit