"Rectitude" has a righteous derivation. It comes straight from the Latin noun "rectus," which means both "right" and "straight." "Rectitude" itself can mean either "straightness" (an early use referred to literal straightness of lines, although this sense is now rare) or "rightness" of character. "Rectus" has a number of other descendants in English, including "rectangle" (a figure with four right angles), "rectify" ("to make right"), "rectilinear" ("moving in or forming a straight line"), and even "rectus" itself (a medical term for any one of several straight muscles in the body).