To sunder means to break apart or separate something, especially in a forceful way.
Sunder can make people think of strong feelings, like anger or sadness, because it's about breaking things apart.
Examples:
The storm will sunder the ship.
He sundered the rope with his bare hands.
The loud noise sundered the quiet night.
I tried to open the bag of chips, but it sundered and they flew everywhere!
The superhero can sunder mountains with his bare hands.
The magician sundered the chains and escaped.