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.
--------
Question: Category: boats 
Words: head, hull, knockout, deck, dock

Answer: knockout


Question: Category: measurement unit 
Words: centimeter, leg, mile, meter, foot

Answer: leg


Question: Category: police punishment 
Words: prison, wispy, flyaway, fine, alert

Answer:
alert