Thames is derived from middle English Temes which itself comes from the Celtic Temasis meaning dark. The "h" was added in the 14th century giving it a Greek look when the Celts were incorrectly believed to have come from Greece (there is a Greek river Thyamis). It is pronounced phonetically - Temz.
Thames Head, which is believed to be the source, is located near Cirencester in Gloucestershire. There is some doubt about whether this is the "true" source of the river several others having a claim (Trewsbury Mead and Severn Springs).
The river Thames (pronounced temz)
The Thames flows through London.
Thames Estuary.
The River Thames flows into the North Sea.
London is on the River Thames but not quite at its estuary.
Gona Thames
Old Father Thames.
Staines-on-Thames is a town located in north Surrey on the river Thames.
river thames
River Thames
The River Thames is wholly within England although there is another river by that name in Canada.
From its Roman name of Tamesis.