According to the OED, “Mettle” is defined as “A person’s character, disposition, or temperament; the “stuff” of which one is made, regarded as an indication of one’s character.” Here, Goneril has just professed her undying “love” for her father and now Regan begins to do the same by stating that she is made up of the same contents as her sister and that their personalities are the same. Furthermore, the word “mettle” adds a significant meaning to the text because it begins to foreshadow Regan and Goneril’s immoral characteristics that are exposed throughout the rest of the play. It is also important to note that although all three sisters are related by parentage, only Goneril and Regan share the same disposition, which sets them apart from Cordelia. (Source: “Discover the Story of EnglishMore than 600,000 Words, over a Thousand Years.” Home : Oxford English Dictionary. N.p., n.d. Web. 15 Apr. 2017.)