Hi, I'd like to know if there is a difference in meaning among the words sweater (made of wool????)
sweatshirt ( made of cotton???)
The way I know it, jumper is a sleevless dress that you can wear on top of a T-shirt.
Now, a difference between a sweater and a sweatshirt:
A sweater is a knitted garment - it can be wool or acrylic or whatever else.
A sweathshirt is usually made from cotton or a cotton/polyester blend and it has a fleecy soft underlining. It's the kind of underlining that absorbs sweat when you work out, hence the name "sweatshirt".