“A tattoo is a form of body modification, made by inserting indelible ink into the dermis layer of the skin to change the pigment. The Oxford English Dictionary gives the etymology of tattoo as, “In 18th c. tattaow, tattow. From Polynesian tatau. In Tahitian, tatu.” The word tatau was introduced as a loan word into English; its pronunciation was changed to conform to English phonology as “tattoo”. Sailors on later voyages both introduced the word and reintroduced the concept of tattooing to Europe.”
Source, more at: fyeahtattoos.com