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.

Example Input: Category: type of rigidity 
Words: rigged, firm, unyielding, streamline, taut
Example Output: streamline

Example Input: Category: aesthetic characteristic 
Words: well, milky, variety, tone, fair
Example Output: well

Example Input: Category: direction 
Words: unhappy, opposite of up, lower, down, sliding
Example Output:
unhappy