TgJ Zec8:12 :וְאַרעָא תִתֵין יָת עֲלַלתַה וֻשמַיָא יְשַמְשוּנוּנוּן בְטַלְהוֹן‏ : the earth will give its produce and the heavens will serve them with their dew
See the entire entry for šmš vb. D to serve