noun, masculineplural: tatarabuelos
great-great-grandfather (great-great-grandmother for the feminine form); great-great-grandparent (either a great-great-grandmother or a great-great-grandfather)
Coined by analogy with tataranieto, and this of tratranieto, of the prefix tras- reduplicated and nieto; formerly trasabuelo was the usual term for our modern bisabuelo. Coromines dates the term around 1625