greenhorn
From Longman Dictionary of Contemporary Englishgreenhorngreen‧horn /ˈɡriːnhɔːn $ -hɔːrn/ noun [countable] informal especially American English someone who lacks experience of somethingExamples from the Corpusgreenhorn• The greenhorns headed out to the corral for their first ride.Origin greenhorn (1600-1700) greenhorn “animal with young horns” ((1400-1500))