What is the sentence proper adjective for joyful?

There isn't a single proper adjective for "joyful." Proper adjectives are capitalized and typically refer to specific people, places, or things.

However, you could use Joyful as a proper adjective if you were referring to something specifically named "Joyful," such as a book title, a company name, or a person's name.

For example:

* "I read the book Joyful last week, and it was very uplifting."

* "Joyful Inc. is a company dedicated to promoting happiness."

If you're looking for a word that describes something that brings joy, you could use words like:

* Joy-inducing

* Joyful (as an adjective)

* Jubilant

* Ebullient

* Exuberant

* Cheerful