This is a powerful word signifying that the person saying it, to put it lightly, JUST DOESN'T CARE! If someone says "Eh" to you, you better start running cause they are in a bad mood, and don't want to be messed with!
Girl #1: GUESS WHAT?!?! I MADE THE SOCCER TEAM!
Girl #2: Eh
Girl #1: Uh-oh....
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