1. Normally a reference to a person's peppy behavior: Jimmy's alacritous behavior was his reaction when his mother told him that he could buy something in the candy store.
2. A quick and cheerful willingness to do something: Dorinda's alacritous acceptance of the invitation to the party surprised her parents.
3. A descriptive term for a certain mood or a tempo of a musical composition, indicating how the music should be played: The concert had several sections of alacritous rhythms.