Read this: The settlement of Plympton, further up the River Plym than the current Plymouth, was also an early trading port, but the river silted up in the early 11th century and forced the mariners and merchants to settle at the current day Barbican near the river mouth. At the time this village was called Sutton, meaning south town in Old English. The name Plym Mouth, meaning "mouth of the River Plym" was first mentioned in a Pipe Roll of 1211. The name Plymouth first officially replaced Sutton in a charter of King Henry VI in 1440. See Plympton for the derivation of the name Plym.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What did Sutton mean in the Old English language?
south town