Primogenitor is a noun that refers to one's earliest ancestor.

Our word of the day is from Latin. It combines the word primo (PREE moe) which means ‘first’ with genitor (JEN ee tore) meaning ‘father.’ You could think of our word of the day as a synonym of forefather or ancestor, but unlike those words, primogenitor may be used to refer to the very first of one's ancestors.

After much searching, we’ve finally discovered our family’s primogenitor in this country. It gives me great pride to single out the first of my ancestors from Ireland.