Barefoot
noun, の adjective
If you have a naked foot, it means you're not wearing anything on your foot, making you barefoot.
The reading here is a bit weird. It's like the words 裸 (はだか) and 足 (あし) were smushed together into one word. The 裸 becomes はだ and the 足 becomes し. You can think of it this way: You were barefoot too long, and because of this, you don't have feet anymore, though you had ashi (はだし) at one point in the past.
水虫になりたくないなら、スリッパを裸足で履かない方がいいですよ。
You shouldn’t wear slippers barefoot if you don’t want to get athlete’s foot.