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: type of sandwich 
Words: club, roll, doorstep, discothek, toast
discothek

Category: secretary duty 
Words: support, type, file, software, answer
software

Category: corporate 
Words: llc, common, firm, solid, private

solid