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: military rank 
Words: sargent, ordinary, captain, colonel, general
ordinary

Category: boxing terminology 
Words: ring, lifeline, deck, punch, corner
lifeline

Category: animal 
Words: fish, iguana, canyoning, hamster, horse

canyoning