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: mode of transportation 
Words: train, spider, wave, fly, drive
Example Output: spider

Example Input: Category: aesthetic characteristic 
Words: fair, unprejudiced, level, tone, milky
Example Output: unprejudiced

Example Input: Category: geographical property 
Words: mansion, valley, smooth, horizontal, flat
Example Output:
mansion