Q: undergarments と underwear はどう違いますか?
A: Undergarments is an old fashioned way of saying underwear. Not in common usage today. I don’t believe I’ve ever heard the word used in a normal conversation.
Q: undergarment と underwear と lingerie と chemise はどう違いますか?
A: undergarment can be anything that is underneath your outer clothes, from a vest, stockings,a t-shirt under ur sweater, to underwear.

underwear= knickers/boxers & bra

lingerie= is just the french word for underwear but it is used in english to mean the same thing....but it only refers to womens underwear,definately don't use it for a guy lol.

chemise= is the silk/satan/lace type vest u wear to bed or under your clothes,a kind of "undergarment" & it's a french word but also used in english sometimes (if you want to be "fancy" ;) & again it's only something women wear