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: type of rigidity 
Words: tough, taut, rough, amalgamated, firm
amalgamated

Category: chocolate food 
Words: fudge, chocolate cake, pudding, unwarranted, heavy
unwarranted

Category: aesthetic characteristic 
Words: fair, ok, cool, texture, ghostly

ok