Where the word "tea" comes from...
All tea comes originally from China so the word "tea" comes from there as well. Tea, in mandarin, is called cha but the dutch traders who first brought back tea in the early 1600s, bought it from traders on junk ships from the port of Amoy in Fujian province. In the Amoy dialect tea is te (pronounced "tay"). Hence the Dutch called it thee and, as they were the first importers of tea, they spread the word as well as the product. From there on, the French called it thé, the Germans thee, it became te for the Spanish, Italian, Danish, Norwegian, Hungarian people, tea in English, thea in Latin, tee in Finnish, teja in Latvian, tey in Tamil and thay in Sinhalese.
For those countries where the tea trade was either originally or mainly via the caravan routes over land, its the Chinese "cha" that is the most common root. It is cha in Japanese, Hindi and Persian, shai in Arabic, ja in Tibetan, chai in Russian and chay in Turkish.