Here's how it works:
* Joy: The root word "joy" means a feeling of great pleasure and happiness.
* -ful: The suffix "-ful" indicates the state of being full of something or having the quality of something.
Therefore, "joyful" means full of joy or characterized by happiness.
The "-ful" suffix is commonly used to create adjectives that describe a state of being full of something, such as:
* Hopeful: full of hope
* Thankful: full of thankfulness
* Beautiful: full of beauty
* Painful: full of pain
* Wonderful: full of wonder