Source : Webster's Revised Unabridged Dictionary (1913)

Jackaroo \Jack`a*roo"\, n. Also Jackeroo \Jack`e*roo"\ [Jack +
   kangaroo.]
   A young man living as an apprentice on a sheep station, or
   otherwise engaged in acquainting himself with colonial life.
   [Colloq., Australia]

Jackaroo \Jack`a*roo"\, v. i.
   To be a jackaroo; to pass one's time as a jackaroo. [Colloq.,
   Australia]