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.

[EX Q]: Category: construction 
Words: excavator, steam roller, concrete pourer, swallow, crane
[EX A]: swallow

[EX Q]: Category: window material 
Words: glass, spyhole, handle, coating, knive
[EX A]: knive

[EX Q]: Category: boxing terminology 
Words: deck, stern, apron, blocking, caution
[EX A]:
stern