c.1300, poucock, from Middle English po "peacock" + coc (see cock (n.)).
Po is from Old English pawa "peafowl" (cock or hen), from Latin pavo (genitive pavonis), which, with Greek taos said to be ultimately from Tamil tokei (but perhaps is imitative; Latin represented the peacock's sound as paupulo).
The Latin word also is the source of Old High German pfawo, German Pfau, Dutch pauw, Old Church Slavonic pavu. Used as the type of a vainglorious person from late 14c. Its flesh superstitiously was believed to be incorruptible (even St. Augustine credits this). "When he sees his feet, he screams wildly, thinking that they are not in keeping with the rest of his body." [Epiphanus]