Given a category and a set of five words, find the word from the set that does not belong (i.e. is the least relevant) with the other words in the category. Words are separated by commas.

Category: elements 
Words: ban, fire, combustion, ground, flame
ban

Category: emotional status 
Words: descending, disgusted, down, miserable, emotional
descending

Category: boxing terminology 
Words: caution, hull, knockout, blocking, deck

hull