disappoint(v = verb.emotion) let down - fail to meet the hopes or expectations of; "Her boyfriend let her down when he did not propose marriage"
is one way to baffle, bilk, cross, foil, frustrate, queer, scotch, spoil, thwart
Derived forms noun disappointment₂, noun disappointment₁
Sample sentences: The bad news will disappoint him; The performance is likely to disappoint Sue

disappoint, v.tr.
1 (also absol.) fail to fulfil a desire or expectation of (a person).
2 frustrate (hopes etc.); cause the failure of (a plan etc.).

Idiom:
be disappointed (foll. by with, at, in, or to + infin., or that + clause) fail to have one's expectation etc. fulfilled in some regard (was disappointed with you; disappointed at the result; am disappointed to be last).

Derivative:
disappointedly adv. disappointing adj. disappointingly adv.

Etymology:
ME f. F d{eacute}sappointer (as DIS-, APPOINT)

VB  be discontented, quarrel with one's bread and butter, repine, regret, wish one at the bottom of the Red Sea, take on, take to heart, shrug the shoulders, make a wry face, pull a long face, knit one's brows, look blue, look black, look black as thunder, look blank, look glum, take in bad part, take ill, fret, chafe, make a piece of work, grumble, croak, lament, cause discontent, dissatisfy, disappoint, mortify, put out, disconcert, cut up, dishearten.

VB  be disappointed, look blank, look blue, look aghast, stand aghast, find to one's cost, laugh on the wrong side of one's mouth, find one a false prophet, not realize one's hope, not realize one's expectation, disappoint, frustrate, discomfit, crush, defeat (failure), crush one's hope, dash one's hope, balk one's hope, disappoint one's hope, blight one's hope, falsify one's hope, defeat one's hope, discourage, balk, jilt, bilk, play one false, play a trick, dash the cup from the lips, tantalize, dumfound, dumbfound, dumbfounder, dumfounder (astonish).