Readings & Meanings:
My shoulders are stiff.
A crack has entered my shoulder blade.
Grass is growing on the shoulder of the road.
月 radical, otherwise known as Tsuki. This is a case where the 月 kanji is standing in for the 肉 kanji, and it refers to flesh. When you see 月 hidden in a kanji, remember, it's probably a word for a body part.
The pictograph in 肩 is pretty straightforward. It's a limb hanging from a shoulderblade.