As a noun:
* The news of her failed audition brought a wave of disappointment.
* His disappointment was palpable when he didn't get the job.
* The disappointment of the cancelled concert was shared by all the fans.
As an adjective:
* He was disappointed to learn that the party had been postponed.
* The children were disappointed with the lack of toys at the park.
* Her disappointed expression said it all.
In a phrase:
* Much to her disappointment, the book was not available at the library.
* To his disappointment, he missed the winning goal.
* The team's performance was a disappointment to their fans.
You can also use "disappointment" in a more figurative way:
* The rain was a disappointment to the picnic plans.
* The lack of sunlight was a disappointment to the garden.
Remember to choose the right form of "disappointment" depending on the context of your sentence.