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.

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

A: summer
****
Q: Category: elements 
Words: water, heat, fire, empower, cool

A: empower
****
Q: Category: construction 
Words: tackle, crane, dump truck, duck, upraise

A:
duck
****