Thesauruses aren't dictionaries. A word is likely to turn up in different places according to which of its various senses is in play.

Folk is a handy word, but when you start trying to shoehorn all the different types of songs we sing into it it is liable to burst at the seams.

"Folk by function" is good. We could have "folk by function" nights in the function rooms at pubs where the clubs used to meet, if we could still find functional pubs...