A word, phrase, or image that returns several times throughout the work, tied to a character or an idea, and gains meaning with each return.
In Julius Caesar
But this same day / Must end that work the Ides of March begun
The "Ides of March" return here: the date announced by the soothsayer in Act I and marked by the murder reappears as the beginning of a "work" that the battle at Philippi will finish. The repetition of the date joins the two poles of the play.