Given a set of five words, generate the word from the set that does not belong (i.e. is the least relevant) with the other words. Words are separated by commas.

Q: fire, cool, water, ban, ice

A: ban
****
Q: ecstatic, specialty, substance, content, merchandise

A: ecstatic
****
Q: firstrate, custody, probation, fine, pretty

A:
pretty
****