Whispered oaths in dark, Bound by shadows' tight embrace, Sealed with mystic ties.

One part of my name is sour, the other has bite, I’m more social than ready to fight.

This word is compound, On top it is found. The first word can be gone, styled, or used to climb down. The second is thin, it can poke in your skin. On your shirt, or a number you hide to punch in.

Legally binding on the desk of a lawyer, Usually for the corner, sometimes on the sides, Use it in the middle and you might get funny looks. What is it?

Paired up with a cat, And oh, what a sound! Four lines of her gut, All so tightly wound...