hi - greeting, 1862, Amer.Eng. (first recorded reference is to speech of a Kansas Indian), originally to attract attention, probably a variant of M.E. hy, hey (c.1475) also an exclamation to call attention. Extended form hiya attested from 1940.
hey - call to attract attention, c.1225, possibly a natural expression (cf. Roman eho, Gk. eia, Ger. hei).
http://www.etymonline.com/h3etym.htm
hey - call to attract attention, c.1225, possibly a natural expression (cf. Roman eho, Gk. eia, Ger. hei).