IPA: /ˌdɪsəˈpɔɪntɪŋ/
KK: /dɪsəˈpɔɪntɪŋ/
Not meeting the expectations or hopes of someone; causing feelings of sadness or dissatisfaction.
The movie was disappointing because it didn't have a good plot.
Disappointing → It is formed from "dis-" (meaning apart or away) and "appoint" (from Old French *apointier*, meaning to arrange or fix). The word "disappointing" means to take away the arrangement or expectation, leading to a sense of letdown or failure to meet expectations.
Think of something that takes away your hopes or arrangements ('dis-') — that's why disappointing means failing to meet your expectations.