This is a device known as gazera shava, which is an “analogy of expressions; that is, an analogy based on identical or similar words occurring in two different passages of Scripture.” (M. Mielzinger, Introduction to the Talmud [New York: Bloch, 1968], p. 143). According to exegetical practice, if one of the passages in which the word occurs is obscure, its meaning is to be ascertained from the other passage.