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: direction 
Words: kind, descending, down, opposite of up, flat
kind

Category: moral characteristic 
Words: precise, grub, frank, stern, honesty
grub

Category: window material 
Words: bowl, plastic, glass, panel, lead

bowl