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: employment activity 
Words: recruit, replace, sack, heat, fire
heat

Category: construction 
Words: digger, concrete pourer, crane, derrick, excavator
derrick

Category: aesthetic characteristic 
Words: fair, level, unprejudiced, variety, size

unprejudiced