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.

Q: Category: consumer product 
Words: merchandise, happy, thing, content, service

A: happy
****
Q: Category: guitar part 
Words: fret, notes, emotional upsets, output cord, truss rod

A: emotional upsets
****
Q: Category: aesthetic characteristic 
Words: color, medium, fair, warm, size

A:
warm
****