This is the kanji for ugetsu: 雨月

It's made up of the characters for rain (雨) and moon (月). It means being unable to see the harvest moon due to rain - the moon being obscured/hazy/misty because of rain clouds. It's typically associated with the fifth lunar month, but sometimes will also be associated with the eighth lunar month.

In the preface of the book it says "I edited this by the window of my study at night with a hazy moon after the rain, and handed it to a publisher. Thus it's titled Ugetsu Monogatari." Monogatari (物語) means tale, story, or legend. So ways to translate Ugetsu Monogatari are: tales of moonlight and rain, tales told under the obscured moon after the rain, the legend of the harvest moon hidden by rain, etc.