'Greenwich' means the green wic, a trading place.
A wic, from Latin vicus, was a trading town or emporium. The name is first recorded as Gronewic in a charter of 918, then Grenewic in 964 and Grenviz in the Domesday Book of 1086. The town later gave its name to the Greenwich Meridian, at 0° longitude, and to Greenwich Mean Time.