When transitional fossils blur previously clear boundaries between major groups, drawing that line can be problematic. While the need to rigorously define formal taxon names is widely acknowledged (e.g., de Queiroz and Gauthier 1992; Cantino et al. 1997), the need for similar precision in the scientific use of vernacular terms is not widely appreciated. The lack of accepted usages for common names has engendered endless arguments about when a fish becomes (also?) a tetrapod (e.g., Clack 1997), when a dinosaur becomes (also?) a bird (e.g., Padian and Chiappe 1998), and when a mammal-like reptile becomes (also?) a mammal (e.g., Rowe and Gauthier 1992). Recent descriptions of fossil snakes with well-developed hindlimbs have raised similar questions about where to draw the line between lizards and snakes and initiated a lively debate over the origin of snakes. However, lack of a precise definition of the vernacular term “snake,” as well as lack of a consensus on what constitutes a higher taxon's “origins,” has seriously hindered discussion of “snake origins.” Here, precise definitions of both terms are proposed and justified and their paleobiological implications discussed. The origin of higher taxa remains one of the most intriguing macroevolutionary problems, but scientists risk arguing at cross-purposes unless they agree on the exact boundaries of vernacular groups, and the exact meaning of the term “origin.”