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: physical activity 
Words: run, jump, autumn, fall, swim
autumn

Category: geographical property 
Words: mountain, flat, hill, mansion, plain
mansion

Category: outdoor sport activity 
Words: swim, horse, climbing, hiking, fish

horse