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: outdoor sport activity 
Words: whale, fish, raft, hiking, kayak
whale

Category: physical activity 
Words: summer, roll, plummet, fall, exercise
summer

Category: accomodation 
Words: even, round, flat, level, smooth

smooth