The word 月 yuè means moon or month and is pronounced like the first two letters in the word “yurt”. It is like the character 日 but with an opening of the bottom. This opening of the bottom implies something not solid, or incomplete, because the moon waxes and wanes.
As 月 signifies the moon, it is the light of night, so 月 is yin energy. Most of the Chinese characters that associate with yin energy have 月 as a component. The spirit is yang, the body is yin, so body parts often have the 月 component, for example 肺 fèi, which means the lungs.