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.
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Question: Category: type of sandwich 
Words: club, roll, doorstep, discothek, toast

Answer: discothek


Question: Category: guitar part 
Words: frustrated, amp, string, fret, headstock

Answer: frustrated


Question: Category: employment activity 
Words: instruct, fire, recruit, let go, cool

Answer:
cool