Spells & Slimes

You have to type one word 

(singular and not conjugated) 
on your keyboard to cast a spell and kill the maximum of slimes.
But you have to find them by yourself !!
Each time you kill a slim, you have to sacrifice one letter from the spells you used. If you use this letter in another spell it will hurt you a little. So you'd better find some synonyms or related words to your fire or water spells !