1. A furry, quite cute (to some) animal that lives in burrows.
2. An spy in the enemy's camp (infiltrator/rat)
3. A black, raised discolouration on the skin
Hope that helped
![Cheesy :D](https://studentforums.biz/Smileys/default/cheesy.gif)
And for the chemical definition u can look it up in any chemistry book. Or google it, about a thousand pages'll come up.