regarding body shape, there is no difference. look at these examples her chance of success was slim, cannot use slender After everyone ate there were slim pickings for the late guests, cannot use slender The spider hung suspended on its slender thread, we would not use slim here.

As adjectives the difference between slender and skinny. is that slender is thin; slim while skinny is (informal) having little flesh and fat; slim; slender; narrow; thin, generally beyond what looks beautiful.