Lean
Slim, Slimming
noun, の adjective
A thin body type is called lean or slim. These days this is usually used in the context of slimming salons and massages you can get that may or may not work.
This is a jukugo word that uses the on'yomi readings of the kanji. You've learned them already, so you should be able to read this on your own!
そのエステは痩身を専門にしているんだって。
I heard the beauty salon specializes in slimming.
一年くらいマッサージに通ったんだけど、痩身の効果はなかったよ。
I kept getting massages for about a year, but I didn't have any slimming results.
防犯カメラに写っていたのは、痩身の男性でした。
The person caught by the security camera was a slim guy.