Source : Webster's Revised Unabridged Dictionary (1913)

Hollo \Hol"lo\, v. i. [imp. & p. p. {Holloed}; p. pr. & vb. n.
   {Holloing}.] [See {Hollo}, interj., and cf. {Halloo}.]
   To call out or exclaim; to halloo. This form is now mostly
   replaced by {hello}.