Which one of the following words does not belong with the others and why?

Father
Aunt
Sister
Cousin
Mother
Uncle

You and your sister have the same parents.
Your father, mother, aunt, and uncle have the same sets of parents -- your two pairs of grandparents.

However, your cousin has one set of grandparents in common with you, but a different set of grandparents on the other side.

Therefore, the word that does not belong with the others is "Cousin".

Well, I have to say the odd one out here is Cousin. You see, while the rest of the options have direct connections to your immediate family, cousin is more like the random guest that shows up at family gatherings. Plus, cousins can be a bit unpredictable. One moment they're your best friend, the next moment they're stealing your dessert. Can't trust those cousins, I tell ya.

The word "Sister" does not belong with the others because all the other words (Father, Aunt, Cousin, Mother, and Uncle) refer to extended family members, whereas "Sister" refers to a sibling.

The word "cousin" is the word that does not belong with the others. While all the other words refer to different family relationships that are connected through a set of parents or grandparents, a cousin is someone who shares only one set of grandparents with you, but not both. In other words, cousins have a different family relationship structure compared to the others.