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: Category: construction 
Words: excavator, crane, pelican, hoist, upraise
Example solution: pelican
Example explanation: A pelican is not related to construction because it is a type of bird.

Problem: Category: personal characteristic 
Words: cool, persistent, assured, ethical, tropical

Solution: tropical