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: corporate 
Words: corporation, firm, synergy, tough, concerted
tough

Category: activity 
Words: blow, waste away, sweet roll, whittle, fritter
sweet roll

Category: weather 
Words: stormy, fair, tangle, variety, luke

variety