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: animal 
Words: train, fly, jump, leap, grasshopper

A: train
****
Q: Category: elements 
Words: ice, fire, burn, let go, combustion

A: let go
****
Q: Category: window material 
Words: wood, metal, glass, frame, plate

A:
plate
****