Origin: Latin suffix -ment
Disappointment has 3 different meanings across 1 category:
a feeling of dissatisfaction that results when your expectations are not realized
"his hopes were so high he was doomed to disappointment"
an act (or failure to act) that disappoints someone
"The sudden cancellation of the concert was a great disappointment to all the fans who had traveled from out of town."
A feeling of sadness or frustration when a strongly held expectation is not met.
"After waiting hours for his favorite team to win, he felt a deep sense of disappointment when they lost in the final seconds."
In plain English: Disappointment is feeling sad when something doesn't happen as you hoped it would.
"The rain ruined our picnic plans, leaving us with great disappointment."
Usage: Use this noun to describe the emotional reaction itself, whereas its verb form disappoint refers to causing that feeling in someone else. Avoid confusing it with similar words like letdown, which often implies a milder, less personal sense of failure.
The word disappointment entered English as a noun formed by adding the suffix "-ment" to the verb disappoint. It originally carried the same meaning it does today, referring to the feeling of sadness when expectations are not met.