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: window material 
Words: glass, coating, panel, spatula, lead
spatula

Category: shady activities 
Words: banned, replace, smear, chocolate cake, fudge
chocolate cake

Category: elements 
Words: blaze, retire, fire, heat, cool

retire