The Origin of the Name

The Thames, from Middle English Temese, is derived from the Celtic name for the river. The name probably meant "dark".
Indirect evidence for the antiquity of the name 'Thames' is provided by a Roman potsherd found at Oxford, bearing the inscription Tamesubugus fecit (Tamesubugus made this). It is believed that Tamesubugus's name was derived from that of the river.
The Thames through Oxford is often given the name the River Isis although historically, and especially in Victorian times, gazetteers and cartographers insisted that the entire river was correctly named the River Isis from its source until Dorchester, Oxfordshire. Only at this point, where the river meets the River Thame and becomes the "Thame-isis" (subsequently abbreviated to Thames) should it be so-called; maps still label the Thames as "River Thames or Isis" until Dorchester. However since the early 20th century, this distinction has been lost in common usage outside Oxford, and some historians suggest the name Isis—although possibly named after the Egyptian mythology is nothing more than a contraction of Tamesis, the Latin(or pre-Roman Celtic) name for the Thames.
For merchant seamen, the Thames has long been just 'The London River'. Londoners often refer to it simply as the river.

Vocabulary:
derive - получать, извлекать, выводить (путем умозаключений)
evidence - ясность, наглядность, очевидность, основание, знак, признак
potsherd - глиняный черепок
feсit - исполнил, сделал (подпись художника)
gazetteer - 1.географический справочник, справка о местности 2. устар. журналист
cartographer - картограф
insist - настаивать
entire - 1. полный, совершенный 2. чистый, незагрязненный
distinction - 1.отличие 2.распознавание 3. уважение
merchant - человек, занимающийся торговлей
refer - направлять, отсылать, обращаться