Use the noun wiseacre when you need an old-fashioned way to talk about a smarty pants. Your grandfather might refer to your smart mouthed, know-it-all little brother as a wiseacre.
Wiseacre and all of its synonyms carry an informal air about them, perhaps suggesting that we don't want to formalize the idea of a smart aleck. Wiseacre comes from Dutch wijssegger, which means "soothsayer." The wise bit is in fact related to wise. The acre part — well, as one dictionary puts it, "the assimilation to acre remains unexplained."