Source : Webster's Revised Unabridged Dictionary (1913)

Shoo \Shoo\, interj. [Cf. G. scheuchen to scare, drive away.]
   Begone; away; -- an expression used in frightening away
   animals, especially fowls.

Source : WordNet®

shoo
     v : drive away by crying `shoo!' [syn: {shoo off}, {shoo away}]