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: guitar part 
Words: fret, worried, chord, notes, headstock
worried

Category: corporate 
Words: unyielding, concerted, firm, combined, united
unyielding

Category: type of sandwich 
Words: picnic, doorstep, club, roll, french toast

picnic