ephemeral

ephemeral
/ɪˈfemərəl; ɪ`fɛmərəl/ adj
living, lasting, etc for a very short time （生存、 持续等）短暂的
    ephemeral pleasures 短暂的欢乐
    Slang words are often ephemeral. 俚语往往只流行於一时.

牛津英汉双解词典