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: activity 
Words: spend, divide, apple, whittle, fritter
apple

Category: elements 
Words: ice, fire, burn, let go, combustion
let go

Category: accomodation 
Words: paved, studio, flat, plain, cabin

plain