Definition of "greenhorn"

The powers of the Canadian voyageurs and hunters in the consumption of meat strike the greenhorn with wonder and astonishment; and are only equalled by the gastronomical capabilities exhibited by Indian dogs, both following the same plan in their epicurean gorgings.

1847, George Frederick Augustus Ruxton, Adventures in Mexico and the Rocky Mountains, page 267

All you greenhorns who wanted to see Covenant up close...this is gonna be your lucky day.

2001 November 15, Bungie, Halo: Combat Evolved, v1.0, Microsoft Game Studios, Xbox, level/area: The Pillar of Autumn

She lives in New Bedford, and her dad's not around much and her mum calls her boyfriend a Portagee, a fuckin' greenhorn,

1993, Common Lives, Lesbian Lives- Issues 47-49, page 37