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: employment activity 
Words: fire, hire, ground, pay, retire
[A]: ground


[Q]: Category: police punishment 
Words: probation, jail, arrest, fine, beautiful
[A]: beautiful


[Q]: Category: type of sandwich 
Words: french toast, submarine, club, convention, hero
[A]:
convention