The let-down of unmet hopes or expectations.
The let-down of unmet hopes or expectations; also a person or thing that fails to meet them.
Defined by the gap between what was hoped or expected and what occurred — a far more specific trigger than the diffuse suffering of misery, woe, or gloom, and much lower in intensity than grief, anguish, despair, or heartbreak. Typically mild-to-moderate and often transient. Sits at the milder, more cognitive/evaluative end of the family (its neighbors are frustration, dismay, dissatisfaction): expectation-driven rather than loss-driven, a setback rather than a shattering.
Noun first attested 1577, from the verb disappoint (mid-15c.), originally “dispossess of an appointed office,” from Old French desapointer “undo the appointment, remove from office.”
The clearest semantic shift in the set: from “undo an (office) appointment” → “fail to keep an appointment / defeat expectations” → the modern emotional sense of unmet hopes (the “frustrate the expectations” sense from the 1570s). No reliable recent-generation shift.