1. A male mallard duck, characterized by its glossy green head.
Usage: common in North American hunting and ornithology contexts
2. A person who is inexperienced or new to a job or activity.
Usage: informal; chiefly North American

Examples

• The hunter spotted a greenhead swimming across the pond at dawn.
• A flock of greenheads migrated south for the winter.
• He was a greenhead on his first day at the construction site.
• Don't worry—every expert was once a greenhead.
• The wildlife guide pointed out the distinctive greenhead among the ducks.