IPA: /ˌdɪsəˈpɔɪntmənt/
KK: /dɪsəˈpɔɪntmənt/
A feeling of sadness or displeasure when something does not happen as expected or hoped.
She felt a deep sense of disappointment when her team lost the game.
Disappointment is formed from "dis-" (meaning apart or away) and "appoint" (from Latin "appointare", meaning to assign or designate). The word describes the feeling of being let down or having one's expectations set apart from reality, as in not receiving what was assigned or expected.
Think of being 'let down' when something you were 'assigned' or expected doesn't happen — 'dis-' means apart, and 'appoint' means to assign.