instruction:
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.
question:
Category: type of rigidity 
Words: rigged, firm, unyielding, streamline, taut
answer:
streamline


question:
Category: type of sandwich 
Words: open-faced, hero, club, discothek, hamburger
answer:
discothek


question:
Category: boxing terminology 
Words: ring, lifeline, jab, deck, knockout
answer:

lifeline