Plural of greenhorn; people who are new to something and lack experience, skill, or knowledge.
From 'green' (inexperienced) and 'horn' (possibly from horns of young animals), first recorded in the 1600s. The phrase likely refers to animals with new, soft horns as a metaphor for inexperience.
During the California Gold Rush, experienced miners called newcomers 'greenhorns'—and they were right to be wary, because greenhorns often made fatal mistakes by not respecting the dangerous conditions!
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