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: unbending, unyielding, inflexible, firm, streamline
streamline

Category: aesthetic characteristic 
Words: prison, fine, there, handsome, high quality
prison

Category: mode of transportation 
Words: fly, bike, car, wave, run

run