means a design or mark made on the skin by inserting ink beneath its surface, intended to be permanent.

from From the Tahitian (and broader Polynesian) word 'tatau,' meaning 'to mark' or 'to strike' — possibly echoing the tapping sound of the tool used to drive pigment in. Captain Cook's crews encountered the practice in the Pacific in the 18th century and carried the word back to English. Curiously, there's an unrelated 'tattoo' meaning a military drumbeat or evening signal, which comes from the Dutch 'taptoe' — literally 'tap shut,' the call to close the beer taps and send soldiers to bed. Two different words, one spelling, both involving rhythm and regret.