In a presidential election, since there are two candidates, (Republican and Democrat) there is often a "third" delegate; someone else running as an "Independent" whom nobody has ever heard of.
I didn't like either of the candidates, so I voted for the third guy.
What I call homo-sapiens addicted to abscesses.
Person 1: Are you addicted to abscesses?
Person 2: Yes.
Person 1: Third Gender
Grandparent's male third cousin.
My third great-cousin-uncle is a good person.
Someone who, in relation to others, has zero parents, zero grandparents, zero great-grandparents and twelve great-great-grandparents in common.